Author: naturehydro

Assuming that tunneling can be taken as an indicator for overall weathering activity, it remains unclear whether the greater weathering activity in the lower fertility sites is due to lower pH, greater nutrient demand on the part of the host, or greater ectomycorrhizal colonization. Hoffland et al. assessed tunneling activity across a northern Sweden podzol sequence and found that the occurrence of tunnels in feldspar grains coincided with the disapearence of easily weatherable cation sources such as biotite. Taken together, these tunnel studies imply a correlative, but not a causative, link between weathering activity by ectomycorrhizal fungi and host nutrient demand. Wilson at al. used magnetic separation to segregate readily weatherable cation sources such as biotite and orthopyroxene from more cation poor K feldpars. They then used a variety of molecular and microscopic methods to asses the density of microbial colonization and weathering state of these minerals. They found significantly more mycelial colonization of readily weatherable cation sources such as biotite and orthopyroxene than on more cation poor K feldpars, but noticed only slightly increased weathering of the biotite compared to the feldspar minerals. In the aforementioned field studies, there is evidence that ectomycorrhizal fungi may increase mineral foraging and colonization in response to increased demand for phosphorus. There is also evidence that weathered tunnels coincide with increased demand for mineral elements other than phosphorus and that ectomycorrhizal hyphae can preferentially colonize mineral fragments which are good sources of mineral nutrients other than phosphorus. However,frambueso en maceta  there is no direct evidence in field studies that foraging for and weathering of K, Mg, or Ca sources by ECM can respond to demand for these nutrients. There are many reports in the literature of forest ecosystems dominated by ectomycorrhizal hosts which, possibly due to anthropogenic acid deposition, are now limited by base cation availability and not nitrogen or phosphorus. The mesh bag approach employed by Wallander and others in Swedish forests may be a good method for examining how the mycorrhizal role in nutrient acquisition has changed with the changing nutrient status of these forests. Especially good sites to use this approach would be the sharp N depositional gradients near industrial or agricultural sites.Microcosm studies allow weathering to be quantified and can focus on the weathering of a single mineral or any desired mineral mix. Microcosms can be used to examine the weathering potential of individual ectomycorrhizal species and can be employed to isolate the weathering activity of the ectomycorrhizal fungus from that of the plant root. Microcosm studies also allow the researcher to isolate the effects of the availability of just one nutrient on weathering activity. In relatively sterile microcosm experiment it is also much easier to assay for readily decomposable weathering agents, particularly low molecular weight organic acids , and examine how LMWOA production affects weathering rates. In soils, measured bulk solution LMWOA concentrations are generally too low to significantly enhance mineral weathering due to their rapid degradation by soil microbiota. However in semi sterile microcosms and at the fungus mineral interface in natural soils, LMWOA concentrations may be high enough to greatly enhance weathering rates via proton promoted and ligand promoted dissolution. Van Scholl et al. looked at how organic acid production was influenced by nutrient deficiency of Mg, N, P, and K. Decreasing P or N increased organic acid production, while reducing Mg or K either had no effect or slightly decreased overall LMWOA, although reducing Mg did increase oxalate production in some treatments. There were also significant differences between individual fungal species organic acid exudation profiles and how they reacted to different nutrient deficiencies. Paris et al. conducted a series of studies examining how weathering activity of ectomycorrhizal fungi in azenic culture is affected by nutrient availability. They found that Ca , K, and Mg had no effect of weathering activity when one element was deficient, however when Mg and K were simultaneously deficient both phlogopite weathering and oxalic acid production increased. In order to test whether weathering activity can respond to nutrient demand there must be a nutrient sufficient treatment and a nutrient deficient treatment, both with added minerals. The great majority of microcosm studies investigating ectomycorrhizal weathering fail to have both a nutrient deficient and a nutrient sufficient treatment. Only the work by van Scholl et al. and Paris et al. , explicitly tested whether weathering activity can respond to nutrient demand. From these studies it does appear that there is potential for the ectomycorrhizal fungus alone, or the ectomycorrhizal seedling to respond to deficiencies in P, Mg, or K by enhancing weathering activity, however the study by van scholl et al. had no added minerals and thus doesn’t actually measure weathering, and the studies by Paris et al. are azenic pure culture studies. More studies are clearly needed to address this specific question. If the ectomycorrhizal fungus is also below its optimal level for a particular nutrient, then increases in weathering or nutrient uptake observed by ectomycorrhizae in a –nutrient treatment are not necessarily a reaction to host plant nutrient demand. Increased weathering may be a reaction to ectomycorrhizal nutrient demand only. Having separate mycorrhizal and rooting compartments would help to resolve this question as would an additional treatment in which the growth medium is kept very nutrient poor but the plant is foliarly fertilized. The two compartment system used in Jentschke et al. would be a very effective way to segregate the ecomycorrhizal nutrient demand from plant nutrient supply. While they do not explicitly test whether weathering activity can respond to changing nutrient status, a number of other studies can offer insight into the study of ectomycorrhizal weathering and some discussion of them is warranted in this review. Ectomycorhizae have been found to increase weathering in a number of microcosm studies ,planta de arandanos en maceta while others have not found any increase in weathering with ectomycorrhizal colonization . Many of these studies find increased weathering with one ectomycorrhizal species but not another or with one nutrient treatment or mineral type but not another. Generally, studies that deny P or K and add a weatherable P or K source such as apatite or biotite do find increased weathering with ectomycorrhizal colonization. The same cannot be said for Mg; no study has yet looked at how weathering by ectomycorrhizal plants is affected by Ca status.Wallander found that all 3 ECM strains tested increased weathering rates above the non mycorrhizal control, but the mechanism of increased weathering was different for each strain: decreasing solution pH , oxalic acid prodution and greater P uptake . The most commonly proposed mechanism for ectomycorrhizal enhancement of mineral weathering is greater nutrient uptake and transport away from the mineral surface . Organic acid production by seedlings is generally found to be altered, though not necessarily increased, by ectomycorrhizal colonization. Organic acid exudation does not respond in a consistent way to nutrient demand or to the presence of certain minerals, nor is it generalizable across different ectomycorrhizal species. When one LMWOA is linked to increased weathering rates it is most commonly oxalic acid. Oxalic acid is produced in particularly large quantities by P. involutus, which also happens to be the most commonly used ectomycorrhizal species in weathering experiments. Ochs et al. found that there were strong weathering agents in the root exudates of H.& crustiliniforme, present in very low concentrations which were likely not LMWOA’s. The work of Calvaruso et al. and Uroz et al. give convincing evidence for a key role that bacteria may play in ectomycorrhizal weathering. They found that bacteria isolated from the symbiotic mantle of ectomycorrhizosphere of oak mycorrhizas have significantly higher weathering capacity than phylogenetically closely related bacteria isolated from the adjacent bulk soil . Calvaruso et al.  demonstrated that one of these bacteria has the potential to enhance non mycorrhizal seedling growth by alleviating Mg and K limitation by stimulating biotite weathering. These results strongly suggest that further research into the field of mycorrhizal helper bacteria and ectomycorrhizal weathering is warranted. It also suggests that some of the highly reductionist experiments with either no bacteria or a much simplified bacterial community may fail to account for a key mechanism of ectomycorrhizal weathering. Often the rooting area in pot or microcosm studies is quite small such that the roots are far more densely packed than they would be in a natural setting. As a result, the ectomycorrhizosphere is no larger than the rhizosphere in nonmycorrhizal treatments. This eliminates one of the major proposed advantages of mycorrhizal colonization, and possibly a key mechanism by which ectomycorrhizae may confer a greater weathering ability on root systems: greater mineral surface contact and uptake of weathering products directly from mineral surfaces. The majority of microcosm experiments employ an artificial rooting medium and/or an inorganic nutrient solution, both of which may be a poor recreation of the nutrient environment of field settings. Nutrient starvation may be achieved when minor nutrient limitation, more representative of field conditions, is desired. Most microcosm studies also have either no or a highly simplified bacterial community, which may significantly alter weathering dynamics from natural settings. Another key drawback of microcosm studies is that the carbon and nutrient exchange dynamics of isolated seedlings in a laboratory may bear little resemblance to that of seedlings or mature trees in the field. In field settings hyphal networks may allow seedlings to avoid some of the initial carbon investment involved in establishing mycorrhizal colonization. Mature ectomycorrhizal trees are generally considered to be dependent on ectomycorrhizal communities for survival, while seedlings in the lab often experience growth reductions in response to mycorrhizal colonization and uncolonized seedlings can be far larger and more vigorous. Calculating the weathering rates in forest soils is critically important to forest managers, air quality policy, and models of forest productivity. Any removal of timber from a forest represents a removal of mineral nutrients; understanding how quickly those nutrients are replenished by atmospheric deposition or mineral weathering is a key component of a sustainable harvesting cycle . Mineral weathering rates determine a soil’s buffering capacity and are the single most important properties determining an ecosystem’s ability to buffer the effects of acidifying pollutants . Mineral weathering rates in soils are also the single most poorly constrained component of models designed to calculate acceptable airborne pollutant loads of nitrogen and sulfur deposition from power generation, transport, and agriculture . Accurate estimates of net primary productivity of forests over the course of the next century are critically important to global carbon models. Forest productivity is predicted to increase due to elevated CO2 . The extent of this negative feedback to elevated CO2 levels is largely dependant on forest trees’ ability to meet their increased carbon availability and water use efficiency with increased nutrient uptake . As the effects of anthropogenic nitrogen deposition continue to accumulate, large areas of forest are limited by base cation availability , which is a function of mineral dissolution. In coniferous trees, elevated CO2 has been shown to increase the ratio of root to shoot biomass  and allocation to mycorrhizal symbionts . To understand how forest productivity and forest carbon stocks will be affected by global change we must first understand whether increased carbon allocation to nutrient uptake organs actually results in increased nutrient uptake and whether this increased carbon allocation is a result of increased nutrient demand. Most forest trees of the temperate and boreal biomes are dependant on ectomycorrhizae for their survival . Ectomycorrhizal fungi  are symbionts that form an intimate association with the fine roots of trees and some woody shrubs. Increased nutrient uptake is generally considered to be the most beneficial effect of EMF on forest trees , though EMF have also been shown to increase water uptake , provide resistance to aluminum and other toxic metals , and increase pathogen resistance . EMF take up nitrogen from the soil and provide their host plant significant amounts of it; up to 80 % of total plant N uptake is from EMF . 

However, ectomycorrhizae have also been shown to provide their host plants with significant amounts of the mineral derived nutrients calcium , potassium , magnesium , and phosphorous . Studies have shown that ectomycorrhizal fungi may also play a role in the weathering of soil minerals, enhancing mineral nutrient uptake from these otherwise highly recalcitrant nutrient pools . Ectomycorrhizal communities are species rich, with well over a hundred ECM species having been documented in monodominant forests , and dozens or more on individual trees . Our knowledge of the respective ecological niches of ECM fungi is poor, but there is ample evidence that suggests discreet, nonSoverlapping niches of habitat preference and nutrient acquisition exist for some species. As atmospheric CO2 concentrations rise, forest growth and tree’s nutrient demands may increase. The Earth’s atmospheric concentrations of CO2 are increasing due to fossil fuel combustion, agriculture, and deforestation, and are predicted to continue to rise, even if we arrest the increasing rate of anthropogenic CO2 emissions. A number of studies have shown that plants grow faster and fix more CO2 when CO2 concentrations are increased above ambient levels . This increased growth however, is dependant on increased nutrient uptake to support increased standing plant biomass There is evidence that forests are responding to this increased nutrient demand caused by CO2SstimulatedSgrowthSenhancement by increasing root growth and developing a deeper distribution of roots.

Anthropogenic nitrogen pollution threatens to alter the productivity and carbon storage of temperate and boreal forests. Anthropogenic nitrogen pollution from energy generation, transport,growing strawberries vertically and agriculture has more than doubled the inputs of nitrogen to terrestrial ecosystems . Emissions of the other major component of acid rain, sulfur, were successfully reduced in the early 1990’s, and public attention to acid rain has since diminished greatly. ANP however, has either remained steady or increased somewhat in the developed world, and has risen sharply, and is predicted to rise even more sharply in the 21st century in the developing world . Nitrogen put into the atmosphere by transport and energy generation returns to earth as HNO3 and can fall as wet or dry deposition many hundreds of miles from pollution sources . Soil nitrogen status is, for temperate and boreal forests, the dominant edaphic factor controlling forest productivity and shaping species composition . Anthropogenic nitrogen pollution has facilitated invasive species establishment in many forests of the temperate and boreal zone and contributed to widespread species loss . There is ample evidence that moderate levels of ANP may significantly increase the net primary productivity of temperate forests . Beyond a certain amount of accumulated ANP forest productivity may drop sharply as a result of soil acidification and excess N inputs leaching out other essential nutrients, which then become limiting to forest productivity. This shift from nitrogen limitation to limitation or coSlimitation by phosphorous , potassium , or calcium due to prolonged ANP has already been observed in a number of forests in Eastern North America. Thus, the continued productivity of forests sustaining heavy nitrogen deposition will become dependant on the uptake of these mineral derived nutrients. Mineral weathering increases the supply of these nutrients and neutralizes the acidifying effects of nitrogen deposition.Decreased below ground carbon allocation equates to decreased inputs of carbon into deep soil; carbon inputs which may lead to longer Sterm soil carbon retention than above ground litter inputs . This decreased below ground carbon allocation also has profound effects on mycorrhizal relations. Understanding how nitrogen deposition and elevated atmospheric CO2 concentrations will affect forest productivity and soil carbon storage is essential to predicting how future anthropogenic emissions of carbon will affect the Earth’s climate. 

At present, an amount of carbon equivalent to 600 % of our annual CO2 emissions is taken up by the planet’s terrestrial biota each year, the majority in forests . Even small increases in forest productivity could be a major negative feedback to greenhouse gasS induced climate change. There is five times as much carbon stored in soils as there is in living plant biomass, a change of just 1 % in soil carbon pools is equal to 3 years of anthropogenic carbon emissions . There is a wide variety of effects of anthropogenic emissions of N and C that may affect these huge stocks of soil carbon, with the net effect, increase or decrease, very much unclear. Ectomycorrhizal communities may play a major role in determining how forest productivity and soil carbon stocks are affected by anthropogenic carbon and nitrogen emissions. Elevated CO2 has been found to alter ectomycorrhizal community composition and increase mycorrhizal colonization . Anthropogenic nitrogen pollution has been found to alter ectomycorrhizal community composition , decrease ECM diversity  and decrease colonization intensity . The potential loss of ECM species from nitrogen deposition reduces forest biodiversity and may represent a reduction in forests’ resiliency to future environmental change. ECM represent a very large sink for fixed carbon; studies have found more than 60% of recent carbon assimilation and net primary production may be allocated to ectomycorrhizal symbionts, though most estimates are closer to 15%.Reductions in C allocation to ECM may significantly reduce soil C storage and serve as a positive feedback to global change. The reductions in carbon allocation to ectomycorrhizae observed under nitrogen limitation may continue as more N deposition occurs or may level off as other nutrients become limiting to forest growth. The increase in below ground carbon allocation observed with elevated CO2 may continue as global CO2levels increase, or may level off or reverse if plants become sufficiently nutrient limited that carbon fixation rates are reduced.

If ectomycorrhizal community shifts observed under elevated CO2 and nitrogen inputs represent a shift towards ectomycorrhizal species that are better able to provide the nutrients most limiting to plant growth, then forests may likely adapt to their shifting nutrient demands and continue to increase in productivity in response to increasing CO2 levels and nitrogen deposition. If, on the other hand, these shifts in community composition, and reductions in mycorrhizal colonization reflect temperate and boreal forests’ adaptation to limitation by nitrogen and only nitrogen,best vetical garden system  then increasing amounts of forest may experience reduced productivity in response to continued nitrogen deposition and the fertilization effect from CO2 enrichment will likely decrease as forests become more severely nutrient limited. My dissertation attempts to shed light on which of these two scenarios is likely to unfold over the coming decades of continued anthropogenic global change. In chapter one, I investigated the effects of nitrogen addition on ectomycorrhizal community composition and colonization in a deciduous forest. Very high levels of nitrogen fertilization significantly changed ectomycorrhizal community composition, decreased ectomycorrhizal diversity, and shifted the ectomycorrhizal distribution more towards the mineral soil. These results suggest that the ectomycorrhizal community may be shifting to meet the changing nutrient demands of the forest and outline a potential mechanism for increased soil carbon storage under anthropogenic nitrogen deposition. Based on the high fungal diversity found in the mineral soil, and the fact that the ectomycorrhizal abundance in the mineral soil increased in response to nitrogen deposition I decided to investigate how the heterogeneous distribution of nutrients in mineral soil determines fungal species distribution. In chapter two, I tried to assess which soil properties determine fungal species distribution. Our sampling design prevented us from assessing the role of some of the chemical properties examined, but carbon content and depth emerged as the most influential soil properties determining fungal community composition. 

Calcium content also appeared to be important in determining fungal community composition. While pure culture studies have shown that ectomycorrhizal fungi vary in their ability to stimulate mineral weathering and take up mineral nutrients, the observed species shifts in ectomycorrhizal communities can only reflect shifting nutrient demands from host plants if plants can allocate carbon to the mycorrhizal fungi that are providing the most mineral nutrients. In Chapter 3, I present a literature review on the current state of knowledge on how plant nutrient demand drives fungal weathering. Within the plant physiology literature there is evidence that plants may be able to respond to phosphorous and potassium limitation with increased carbon allocation to mycorrhizal fungi providing those nutrients. Magnesium limitation reduces below ground carbon allocation, and the effects of calcium limitation on carbon allocation are unclear. In studies of ectomycorrhizal weathering there is a distinct lack of explicit testing of the role of host nutrient status in driving fungal weathering. I conclude by making a number of recommendations for how future studies can address this important question. For the fourth chapter of this dissertation I investigated how elevated CO2 affects plant growth, biotic weathering, and organic acid exudation, as well as the roles of plants, their ectomycorrhizal symbionts, and organic acids in stimulating mineral weathering. Elevated CO2 increased plant growth but did not increase mineral weathering. Pine seedlings but not ectomycorrhizae significantly increased mineral weathering, though there was some indication that one of the two ectomycorrhizal species examined, Piloderma&fallax, may have stimulated mineral weathering. These results do not support the hypothesis that increased nutrient demand by plants, caused by increased CO2 availability, will stimulate weathering, though our system’s departures from forest soil conditions hamper our ability to directly relate our results to processes in forested ecosystems. In my doctoral research I set out to determine whether the ecological, chemical, and physiological nature of the ectomycorrhizal symbiosis will allow for ectomycorrhizal communities to shift their functioning in accordance with the changing nutrient demands of forests experiencing global change. My research indicates that ectomycorrhizal communities may shift to accommodate the shifting nutrient demands of forest undergoing sustained heavy nitrogen deposition, but failed to find an effect of elevated CO2 on mycorrhizal fungi or biotic weathering. I also identified a number of ways in which future studies could address these questions in a more targeted, verifiable manner.Anthropogenic nitrogen pollution is a global problem that threatens the ecological integrity of many terrestrial and aquatic ecosystems. Anthropogenic nitrogen pollution  from energy generation, transport, and agriculture has more than doubled the inputs of nitrogen to terrestrial ecosystems . Emissions of the other major component of acid rain, sulfur, were successfully reduced in the early 1990’s and public attention to acid rain has since diminished greatly. Anthropogenic nitrogen pollution however, has either remained steady or increased somewhat in the developed world, and has risen sharply, and is predicted to rise even more sharply in the 21st century in the developing world . Nitrogen pollution from agriculture either leaches into streams, lakes, and groundwater as nitrate or volatilizes off of fields and manure deposits to return to the earth in the form of ammonium. Nitrogen put into the atmosphere by transport and energy generation returns to earth as HNO3 and can fall as wet or dry deposition many hundreds of miles from pollution sources. As a result of both these processes, but primarily due to the more far reaching HNO3 , large forested regions are receiving inputs of HNO3 that threaten to dramatically alter their ecology and species composition , and, when prolonged severe deposition occurs, reduce their productivity.Ectomycorrhizal fungi are essential to forest health and are particularly important to the nitrogen nutrition of temperate and boreal forests. They form intimate associations with tree roots, providing the roots with nutrients and receiving fixed carbon from their plant hosts. Ectomycorrhizae form symbiosis with less than 3% of the world’s plant species but with many of the dominant trees of temperate and boreal forests, particularly the plant families Pinaceae and Fagaceae, . Ectomycorrhizal communities are species rich, with well over a hundred ECM species having been documented in monodominant forests , and dozens or more on individual trees . Ecomycorrhizae have been shown to transfer significant amounts of P , Mg , Ca , and K to their plant hosts, but their provision of nitrogen is generally considered their primary contribution to plant health.Studies have shown that ECM may provide up to 80% of a host plant’s total N uptake . The extraradical mycelia of ECM greatly increase the volume of soil that roots can exploit . Through the use of a diverse suite of enzymes ECM may be able to solubilize and take up nitrogen from organic N pools that roots cannot utilize .

Furthermore, linear regression shows a decreasing change in slope from CF treatment to MS and HS treatments which is explained by the non linear sorption of As and the different forms of Fe in plaque , demonstrating that Fe in the CF treatment has a higher affinity for As in comparison with II treatments. In Chapter 1, our results demonstrated that total grain As concentrations are higher in the CF treatment in comparison to II. In addition, we found that iron plaque in the CF treatment can bind greater amounts of As . Overall, more As is present and mobilized in rice plants under continuous flooding. Therefore, we postulate that under II the main mechanism for reducing As accumulation in grain is not directly its sequestration in the rhizosphere but rather the oxidation and immobilization of As in bulk soil which drives the observed sequestration in the rhizosphere. Nevertheless, changes in the mineralogy of root plaque play a key role in reducing the accumulation of As in grain. Elucidating the abiotic changes in Fe and As chemistry that occur in soil due to II facilitates our understanding of the mobilization and bio availability of As in rice paddies. However, research on the concurrent biotic impacts on As bio availability and soil health with II is required and this information should be included in a conceptual model for As mobility and bio availability in rice.Rice plants readily take up and accumulate arsenic in the grain when grown in flooded paddy fields, posing a threat to human health . Intermittent irrigation has been a subject of increasing interest due to its efficacy in reducing As accumulation in rice, reducing methane gas emissions, and increasing water use efficiency during rice cultivation . II is characterized by a distinct cycling of flooded and non flooded periods that are accompanied by redox fluctuations, which have a significant impact on the fate and form of certain contaminants and nutrients in soil,container vertical farming as well as soil microorganisms . The cycling of redox active elements in soil is often associated with abiotic factors such as mineral precipitation and reductive dissociation; or biotic factors such as the activity of plant roots and related microorganisms .

The biogeochemical cycle of As is linked to microbial mediated transformations and influences the mobility, distribution, and availability of As species in the environment. In rice paddies, microorganisms play vital roles in both aerobic and anaerobic soil conditions. During continuously flooded treatments, some anaerobic bacteria can use AsV as a terminal electron acceptor in respiration and subsequently reduce it to AsIII, contributing to greater As bio availability in the soil solution . In aerated soils, some aerobic bacteria can transform AsIII to less toxic forms, such as AsV and methylated As . Arsenic reducing and oxidizing bacteria often coexist in the rice rhizosphere, and their abundance and activities regulate As speciation, bio availability, and accumulation in rice paddies . The relative abundance and activity of As transforming microorganisms are key factors that influence the fate of As in paddy soils, and consequently the bio availability of As to rice plants . Moreover, it is well documented that numerous bacteria species are involved in iron oxidation within the rhizosphere, and thus the microbial community may also play an important role in Fe plaque formation . Dissimilatory iron reducing bacteria use FeIII from iron oxide minerals as a terminal electron acceptor during anaerobic respiration. This reductive dissolution reactions facilitates the release of As from iron oxides, increasing its bio availability for rice uptake. On the other hand, the oxidized micro environment created by the oxygen secreted from rice aerenchyma allows iron oxidizing bacteria to couple the oxidation of FeII with the reduction of a variety of electron acceptors, promoting the co precipitation of As with iron oxides .Microorganisms are very sensitive to small changes in their environment and can be influenced by a range of biotic and abiotic factors . It is thus expected that redox fluctuations caused by II events will affect microbial activity and succession in the rhizosphere. II is a promising management strategy for reducing As concentrations in grains but needs to be accepted by rice growers for widespread adoption in rice cultivation. Scarcity of information withholds farmers from making well informed decisions. Although growers are typically most concerned about how changing on farm operations will affect their agronomic systems, there remains a need for mechanistic biotic and abiotic information to explain broad implications of establishing II treatments.

At present, the impact of microbial processes on As cycling in the rhizosphere is not well understood. Thus, there is a need for studies that investigate the association between water management treatments, changes in soil microbial communities, and the influence of bacteria in As and Fe cycling in rice systems. Studies that analyze the impact of II on microbial community composition often report treatments with several dry down events and yield is not always evaluated . Understanding the changes of microbial populations due to paddy water management regimes can provide information about the role of rhizosphere bacteria in Fe plaque formation and As speciation, bio availability, and mobility in rice systems. The primary objective of this study was to reproduce rice field conditions in a series of pot based bio assays with single dry down II treatments of varying severity and to observe the effect of water management fluctuations in rhizosphere soil bacterial communities throughout the growing season. The experimental design aimed to replicate the field conditions from the field based irrigation management rice growth trials conducted at the California Cooperative Rice Research Foundation Rice Experiment Station in Biggs, CA during summer 2017 and 2018 . The current study was conducted in Escondido, CA during summer 2020. The site has a Mediterranean climate with an average temperature of 20.6 °C and average precipitation of 0.813 mm for May  October 2020. Soil from the RES was collected,hydroponic vertical garden mixed to homogenize, and placed into 1 gallon pots. The average As and Fe concentrations in the soil were 3.87 mg kg 1 and 33.39 g kg 1 , respectively. The three II treatments were high, medium, and low severity ; and one continuously flooded as a control. Each treatment was assigned to a 62 L plastic bin that contained 6 replicates of 1 gal pots with paddy soil. Rice seeds were planted evenly on the soil surface and the bins were flooded 10 cm above the soil line. Every 5 days water was added to reach the initial water level, pH and redox potential were measured, and bins were re oriented and repositioned based on a randomized complete block design . For the dry down events, the water from the three II bins was drained and soil moisture was measured on an hourly basis utilizing a Watermark handheld meter and soil moisture sensors set at a depth of 10 to 15 cm. Soil was sampled throughout the season on similar dates from the field experiment presented in Chapter 1. Table 3.1 provides the timeline for sampling, water treatment management, and other events throughout the experiment. Soil was collected using a 1 mL sterile syringe with the end tip cut off to create a miniature soil probe. Approximately 1 g of soil was obtained at a depth of 5 10 cm at the base of the rice plants , and two samples were obtained from each pot. A 0.25 g sub sample was separated, and DNA was extracted with the Qiagen DNeasy PowerLyzer PowerSoil Kit. At harvest, the rice grain was collected, and plants were rinsed to remove soil adhered to the roots. Roots were separated from the shoots and washed thoroughly with DI water to remove any remaining soil. All plant biomass was dried at 65 °C for 24 h. Paddy grain was polished into white grain utilizing a rice huller and mill, and each layer was ground, sieved at 0.5 mm, and stored in airtight containers. Roots and shoots were cut into 2 cm sections and a 5 g sub sample was ground and sieved at 0.5mm and stored for further analysis. DNA extractions and library preparation were performed by the UC Davis Host Microbe Systems Biology Core Facility.

Primers 341F and 806R were used to amplify the V3 V4 domain of the 16S rRNA using a two step PCR procedure. Step one was the amplification procedure where the primers contained an Ilumina tag sequence, a variable length spacer, a linker sequence and the 16S target sequence. In step two, each sample was barcoded with a unique forward and reverse barcode combination using forward and reverse primers. The final product was quantified on a Qubit instrument using the Qubit High Sensitivity dsDNA kit and individual amplicons were pooled in equal concentrations. The library was quantified via qPCR followed by 300 bp paired end sequencing using an Illumina MiSeq instrument and taxonomic groups were assigned using the Silva rRNA database. Data of quantified As and Fe in plant biomass, all treatment effects, and differences between sampling dates were assessed using a two way analysis of variance . All effects with p values < 0.05 were considered significant. P values are presented throughout, but where significance is discussed, Tukey’s multiple comparison test was conducted. Relationships between samples from microbial analysis were visualized using principal coordinate analyses obtained based on Bray Curtis dissimilarity metrics.Consistent with results presented in Chapter 1, II treatments decreased As concentrations in rice grains, shoots and roots, and increasing dry down severity had a greater impact in reducing As bio accumulation . Like As, the concentration of Fe in root samples with plaque was highest for CF treatment and decreased for LS, MS, and HS treatments . It is surmised that dry down events promote oxic conditions in the bulk soil and aqueous FeII is oxidized and immobilized via precipitation of FeIII oxides, decreasing the overall Fe content in the rhizosphere and root plaque compared to the CF treatment. With CF, mobile aqueous FeII persists in the bulk soil and is oxidized only after being transported into the oxygenated rhizosphere. Therefore, greater precipitation of FeIII oxides as root plaque occurs, and a higher total Fe concentration is observed in root samples from the CF treatment. Soil pH continually increased from sowing to harvest by 1.5 units . This increase is explained by the constant consumption of protons in paddy soils during reduction processes associated with flooded rice paddies . Soil redox potential dropped upon initial flooding, increased above 100 mV during dry down events, and declined after reflooding below 300 mV for all treatments . This pattern indicates oscillation between anoxic and oxic conditions. The redox state of Fe and As during these fluctuations can be predicted via the Nernst equation or, simply, by utilizing the pH and Eh measurements and referring to Pourbaix diagrams, which indicate that both As and Fe are present in their reduced forms during flooding and become oxidized during the dry down events of II treatments . During the dry down periods in the three II treatments, soil water potential reached 10, 70, and 120 kPa for LS, MS, and HS treatments, respectively. Based on Carrijo et al., 2018, soil water potentials reached during dry down events are equivalent to volumetric water contents of 40, 35, and 25% for LS, MS, and HS, respectively. These parameters were carefully defined for the field trials, as well as the timing of the dry downs, to ensure that rice plants reach maturity and maintain yields . From 52 identified phyla, the 15 most abundant accounted for 98% of the total sequential reads. The three dominant phyla for all treatments throughout the growing season were proteobacteria, actinobacteriota, and acidobacteriota, which are typically found in agricultural soils . Proteobacteria, the most abundant phylum in our soil samples, is expected tothrive in carbon rich environments, such as rice paddies . Although the mentioned phyla predominated in our samples, there were variations in the relative abundance of these groups. Our samples from the CF treatment express a higher abundance of the phyla actinobacteriota and firmicutes, whereas acidobacteriota, chloroflexi, and myxococcota are more abundant in the HS treatment. These results suggest phylogenetic differences in the bacterial communities are driven by fluctuations of anoxic and oxic conditions.

The Arabidopsis CLE gene was found to be induced by N deficiency, and over expression of CLE inhibits lateral root elongation but not initiation. The peptide sequence of CLE is homologous to CLV3, which binds to CLV1 and the clv1 mutant showed increased lateral root length under low N conditions. The transcript levels of CLE were increased in the clv1 mutant, suggesting a feedback regulation of CLE by CLV1. Transgenic lines with increased CLE levels in clv1 did not inhibit lateral root growth, indicating that the inhibition of CLE3 on lateral root development requires CLV1. Altogether, the N responsive CLE CLV1 peptide receptor signaling module restricts expansion of the lateral root system in N deficient environments. Although nitrate is a crucial nutrient and signaling molecule, its distribution in soils is heterogeneous. To adapt the prevailing nitrate conditions, plants have evolved a systemic response mechanism. NRT2.1 was the first molecular target identified in long distance signaling reflecting root responses to environmental nitrate conditions. Plants were grown using a 1 mM NO3 − solution, then the root was split into two parts, one subjected to N free treatment and the other one treated with 1 mM NO3 −. Both 15NO3 − influx and the transcript level of NRT2.1 were increased in the NO3 − fed root. Recent findings revealed that the C terminally encoded peptide originated from N starved roots; located in xylem vessels, it sends root derived ascending signals to the shoot before being recognized by a leucine rich repeat receptor kinase, CEP Receptor 1 , and then inducing the expression of CEPD polypeptides. CEPD sent long distance mobile signals translocated to each root and upregulated the expression of NRT2.1. The activity and expression of NRT2.1 in plants were inhibited when supplied with high N. Lepetit’s lab configured a forward genetic approach using a transgenic line expressing the pNRT2.1::LUC construct as a reporter gene. The mutant hni9, showing increased expression of NRT2.1 under high N supply,vertical growing systems was isolated and the mutation was found in IWS1, a component of the RNAPII complexes.

Further investigation revealed that the levels of the H3K27me3 on NRT2.1 chromatin decreased, resulting in the upregulated expression of NRT2.1 in response to high N supply in the iws1 mutants. Thus IWS1 is likely to be involved in the transduction of N systemic signals through controlling the expression of NRT2.1 in plants. Another important player participating in root foraging, TCP20, was identified by Crawford’s lab using the yeast one hybrid system to screen the transcription factors that can bind to the fragment of nitrate enhance DNA. TCP20 was found to be able to bind to the promoters of NIA1, NRT1.1, and NRT2.1. The tcp20 mutants exhibited deficiencies in preferential lateral root growth on heterogeneous media in split root experiments, indicating that TCP20 can regulate the preferential growth of lateral roots in high nitrate zones, thus playing an important role in the systemic signaling pathway. Recently, using an electrophoretic mobility shift assay , the DNA binding sites of TCP20 in a 109 bp NIA1 enhancer fragment were found to be in close proximity to NLP7 and NLP6 binding sites. Yeast two hybrid and bimolecular fluorescence complementation assays showed that NLP7 and NLP6 can interact with TCP20 and both the PB1 domains of NLP6&7 and the glutamine rich domain of TCP20 are necessary for protein–protein interaction. Further work will be needed to elucidate the underlying molecular mechanism explaining the involvement of TCP20 in systemic signaling.Root microbiota associate with every land plant and show community compositions and dynamics that are distinct from the surrounding soil microbial community . Both rhizosphere and root endosphere microbiomes affect plant health and soil health via processes such as mineral and nutrient turnover and pathogen suppression . Attribution of specific processes to distinct microbial players or populations is challenging because soil ecosystems are among the most complex environments on Earth . Soils are made up of a multitude of heterogeneous abiotic and biotic components that interact in a dynamic fashion over a range of spatial and temporal scales .

Soil type, together with climatic characteristics, allows for the development and activity of biological constituents that are specific to a given soil in a particular location and can vary dramatically among soils and locations . Those biological constituents can include plants, insects, bacteria, archaea, and fungi, which all contribute to and feed off of the bio geochemical cycles in a given soil. The resulting complex network of interactions is extremely challenging to disentangle due to technological limitations and insufficient information in biological and chemical reference databases . Furthermore, soils contain a vast diversity of microorganisms, which are heterogeneously distributed and engage in frequent horizontal gene transfer. Despite this, most root microbiome studies present data from single time points or single locations and primarily conduct amplicon sequencing combined with limited information on plant or environment. Although the average values provided by such studies may suggest some interactions or mechanisms, few studies follow up with the comprehensive sampling necessary to definitively understand these mechanisms and interactions. In addition, single point studies are difficult to compare or extrapolate to other environments or plants because measured values can vary dramatically over time . Soil and other environmental characteristics can be important indicators of biogeochemical processes that have occurred in the past or are ongoing. Generally, few root and soil microbiome studies take advantage of the relatively inexpensive techniques to measure soil characteristics. Data on parameters such as pH, volumetric water content, temperature, and salt concentration could allow researchers to draw correlations between microbial activity, plant productivity, and environmental parameters and facilitate opportunities to cross reference studies conducted under comparable conditions.

In the last decade, the root microbiome research community has made tremendous progress in understanding the complexity of soil ecosystems through improvements in experimental methods at both laboratory and field scales.This review summarizes recent technological advancements and the resulting research opportunities categorized by ecosystem component and scale ,outdoor vertical plant stands and ends with an outlook and potential applications for phytobiome research.Microbial colonization of the root and rhizosphere can significantly affect root phenology and metabolism. Roots demonstrate enormous phenotypic plasticity with respect to anatomy, shape, cell type, cellular structure, metabolism, and biochemical composition, and these characteristics contribute tremendously to root exudation variation and, as a result, to microbial community differentiation . These reciprocal interactions between roots and microbes are not well understood but their direct link showcases the fact that, for understanding root microbiomes, a foundational understanding of root biology is required. Although hyperspectral imaging of leaves has been broadly applied to monitor plant health, even simple imaging of intact roots has lagged behind due to the challenges presented by the opaqueness of soil . Ideally, imaging of root architecture, microbes, and chemical composition as well as visualization of fluxes such as carbon flow through plant compartments and into the soil would be conducted at multiple temporal and spatial scales. Most current methods for analyzing root growth either require artificial growing conditions , are severely restricted in the fraction of roots detectable , or are destructive . For example, many root phenotypic datasets have employed coring or “shovelomics”, subsequent root picking and washing, and imaging using light imagers such as the RhizoVision Crown platform . This method provides valuable information about root architecture; however, it is extremely laborious, it is often not feasible to excavate deep roots, it can remain unknown how much of the root system was recovered and scanned, and root excavation often times terminates the experiment for the selected plants. All of these methods are severely limited because they are destructive, low throughput, or artificial. The later point is particularly important because root architecture can be significantly affected by plant genetics, environmental conditions, soil type, and root colonizing bacteria and fungi . Magnetic resonance imaging presents a noninvasive modality that addresses some of the limitations of other root measurement techniques. When coupled with an analysis pipeline in an automated system, MRI can monitor root mass, length, diameter, tip number, growth angles , and spatial distribution in a high throughput manner . Similarly, X ray computed tomography scanning can provide a comprehensive picture of root systems as long as the roots have a diameter larger than the instruments’ resolution . Hence, small plants or young roots are not likely to be resolved well. Another limitation common to both MRI and CT technology is that plants must be grown in pots that fit into the imaging machines and the applicability of MRI and X ray CT in three dimensional imaging of root systems across various pot sizes was recently evaluated . Although both MRI and CT were able to resolve high quality 3D images of root systems in vivo, the reconstructed length and image details differed significantly between the two methods. In small pots, CT outperformed MRI and provided more details thanks to higher resolution whereas, in large pots, MRI was able to display root systems more comprehensively than CT.

Soil features such as minerals and burrows can be resolved with CT, while MRI can measure water content in roots and soil. Both CT and MRI, struggled with roots thinner than 400 mm .Using Synchrotron X ray microtomography, Milien et al. contrasted the 3D images of vascular systems of successful and unsuccessful graft interfaces in vine rootstocks. Others have applied synchrotron X ray microtomography to visualize drought induced embolism in various plant species , to correlate root hair with rhizosphere soil structure formation , and to quantify root induced changes of rhizosphere physical properties . Although synchrotron X ray micro CT can render unprecedented detail into the microanatomy of plants and microorganisms, the focus window is relatively limited and biological samples tend to lose viability as a result of the intense X ray radiation. There are various other imaging methods that have been recently developed or applied to phytobiome research, including super resolution confocal imaging, which can enhance 3D mapping of root and microbial or fungal cells and showcase green fluorescent proteins , and correlative confocal and focused ion beam tool with integrated scanning electron microscope, which allows for extremely fine scaled 3D mapping . When applied individually or in combination, the above mentioned imaging methods will provide opportunities to visualize plant tissue and attached or internally residing bacteria, fungi, and viruses at unprecedented resolution, as well provide information about their physical and chemical context. Because root development is vital for plant health, expansion of root image databases and novel correlations between above and below ground plant features will enhance our understanding of plant response to environmental and biological stimuli.An important goal of the plant microbiome field is to discover beneficial or deleterious effects of microbes. This means that recording and understanding plant phenotypes and linking them to microbiome variation is key. Similarly, plant microbiomes are intimately tied to the background soil; hence, monitoring soil characteristics is important but can be challenging and labor intensive at appropriate temporal or spatial scales.Unmanned aerial vehicles equipped with RGB cameras, infrared cameras, multi spectral and hyperspectral cameras, GPS, navigation systems, programmable controllers, and automated flight planning have emerged as powerful tools for nondestructive, high throughput field phenotyping that can be performed throughout the growth season . This has removed a bottleneck in phenotyping but automated processing of this data still presents various challenges, which are discussed elsewhere . Monitoring of agricultural fields using drones has become popular among researchers to more accurately plan and manage their experimental operations. Drones can produce precise maps of soil characteristics and plant characteristics , as well as determine irrigation needs, nitrogen levels, and pest occurrence . RGB, IR, and hyper as well as multi spectral cameras attached to drones can collect images of the above ground portion in a range of wavelengths. The resulting data can produce, for example, a vegetation index describing the amount of wavelengths of light emitted from a crop and, hence, can trigger irrigation systems or evaluate the sensitivity of crop breeds to soil moisture in a high throughput manner . Image data can also provide information about plant health status over time and in dependence on the field location and, thereby, allows the employment of an early warning and response system to plant disease or stress .

Rhizobiomes are influenced by their spatial orientation towards roots in two ways. First, the radial proximity of microbial communities to roots defines community complexity and composition, as described in recent publications, and as outlined by the two step model ofmicrobial root colonization mentioned above. Second, the lateral position of microbes along a root shapes the community, as exemplified by early studies. Importantly, recent microbiome studies take into consideration the former, but not the latter aspect. In this section, we discuss specific microbial associations with various root regions, and the role of spatially distinct root exudation. Root tips are the first tissues that make contact with bulk soil: root tips are associated with the highest numbers of active bacteria compared with other root tissues, and likely select microbes in an active manner. The root elongation zone is specifically colonized by Bacillus subtilis, which suggests a particular role of this zone in plant–microbe interactions.Their community includes decomposers, which could be involved in the degradation of dead cells shedding from old root parts. Similarly, lateral roots are associated with distinct microbial communities, differing between tips and bases, as well as between different types of lateral root. One trait influencing the differential microbial colonization of root tissues could be the differential exudation profiles of the distinct root parts. This is illustrated in the following example. Clusterroots are densely packed lateral roots formed by some plants growing on extremely nutrient poor soils; these roots exude high amounts of organic acids and,nft vertical farming in some cases, protons, to solubilize phosphate.

The low pH and carboxylate rich rhizosphere of cluster roots is associated with a specialized rhizobiome, dominated by Burkholderia species that metabolize citrate and oxalate. Besides organic acids, mature cluster roots also exude isoflavonoids and fungal cell wall degrading enzymes, leading to a decrease in bacterial abundance, as well as fungal sporulation. Taken together, cluster root exudates not only solubilize phosphate, but also regulate microbes in such a way that they do not interfere with phosphate uptake. Beyond this example, spatial patterns of metabolite exudation are largely unexplored.We hypothesize that such patterns exist in all root systems for the following reasons: spatially distinct organic acid exudation is atrait of all root systems ; spatially distinct exudation was similarly detected for strigolactones, amino acids, and sugars; and root nutrient uptake, which is sometimes coupled with proton transport, can also exhibit spatial patterns . Overall, spatially defined metabolite exudation by distinct root parts is likely an important factor in structuring the rhizobiome. Future studies should aim at characterizing spatially distinct rhizobiomes and their functional traits, and at investigating spatially distinct root exudation.Roottips are not only associated with high numbers of bacteria , but also produce border cells and mucilage , crucial for plant–microbe interactions. Depending on the root meristemorganization,border cells are released into the rhizosphere either as single cells or as border like cells .Residence time in the soil is different for the two types of border cell. Single maize border cells stayed alive in soil for months, likely due to the presence of starch deposits, whereas arabidopsis border like cells survived for only 2 weeks. Border cells have a transcriptional profile distinct from root tip wells, with overall lower primary and higher secondary metabolism. ABCtransporters constitute a large fraction of differentially expressed genes, which is consistent with transport of secondary metabolites. Secondary metabolites are likely central to the role of border cells in defense against pathogens.

Pathogen attack can result not only in higher border cell production and release, but also in higher mucilage production by border cells and root tip cells. Mucilage contains proteins with antimicrobial functions, as well as extracellular DNA involved in defense against fungi and certain bacteria. Importantly, mucilage is also produced under nonpathogenic conditions, serving as a lubricant for the root environment and stabilizing soil particles. Interestingly, mucilage also provides distinct carbon sources for microbes, thus influencing rhizobiome composition. Border cells similarly interact with nonpathogenic microbes : they release flavonoids that attract rhizobia, uncharacterized compounds that induce branching of mycorrhizal hyphae, and arabinogalactans that trigger biofilm formation of specific beneficial bacteria. The full extent of how border cells and mucilage shape root–microbe interactions remains unclear. It is tempting to speculate that the specialized metabolism of the border cells results in a distinct exudation profile of not only proteins and mucilage, but also low molecular weight compounds that could serve as microbial nutrients or as signaling compounds. Further research should focus on the genetic and physiological differences between border cells and border like cells, as well as on the transport proteins involved in exudation of low molecular weight compounds, DNA, and proteins.Plant–microbe interactions are not only defined by plant root morphology and plant derived exudates, but also by microbe–microbe interactions . Thus, we focus further here on microbial communities. Specififcally, we discuss: how plant exudates influence microbial diversity; how plant responsive microbes are identified; how microbes interact and how mycorrhizal fungi influence root–bacteria interactions. The rhizosphere serves as carbon rich niche for the establishment of microbial communities, in contrast to bulk soil, which is rapidly depleted in carbon and other nutrients by heterotrophic microbes.

Given that the ability of microbes to metabolize plant derived exometabolites might determine their success in the microbial community, several studies have investigated whether the diversity of plant exudates correlates with microbial diversity. Some studies found higher plant diversity was associated with higher microbial diversity, and that the addition of a diverse exudate mix to plant monocultures increased microbial diversity. Interestingly, isolates from soils with a diverse plant community consistently exhibited less narrow niches and displayed less resource competition than did isolates from low plant diversity environments. Although on a global scale, environmental factors had a larger impact on microbial diversity than did plant diversity, we can conclude that, on a local scale, high plant diversity likely promotes a diverse microbial community.The large diversity of microbial communities is a current challenge for plant–microbe research, because it is impractical to study questions such as how members of a community interact, and what specific traits a microbial community has. Therefore,indoor vertical farming many studies currently aim at identifying the subset of microbes responsive to plants. Strikingly, only 7% of bulk soil microbes increased in abundance in the rhizosphere compared with bulk soil, which reduces the number of taxa to investigate from thousands to hundreds. Other approaches to identifying plant responsive microbes have focused on transcriptional profiling. Compared with soil abundant microbes, plant associated microbes exhibited distinct transcriptional responses to plant exudates and, intriguingly, displayed distinct phylogenetic clustering. Network analyses further revealed that rhizosphere microbes displayed higher levels of interactions than did bulk soil microbes. These studies illustrate the potential for the identification of a distinct set of plant responsive microbes. The above points highlight how plants influence microbial communities. However, the members of microbial communities also interact with each other. Compellingly, it is still unclear whether microbe–microbe interactions are predominantly positive or negative. Network analyses reported predominantly positive intrakingdom interactions. By contrast, laboratory growth assays identified competition as the major factor in shaping isolate communities, and cooperation could only be detected for 6–10% of the isolates. One major difference between the two experimental approaches is that the former investigates a natural system, whereas the latter is based on the ability to culture microbes. Isolation of microbes introduces a bias, since it can select against cooperators, precluding obligate syntrophs. Further evidence that at least some microbes avoid competition was provided by co cultivation experiments.

Environmental isolates: displayed high substrate specialization; did not necessarily take up the compound with the highest energy; and diverged in substrate use when cultivated for several generations. In addition, some metabolites exuded by microbes could be metabolized by others, suggesting potential cross feeding between community members. The above findings suggest complex interactions of microbes. It remains to be resolved in which situation competition or cooperation dominates communities. However, it is evident that microbial interactions are based on altered gene expression. Microbes responded to competing bacteria or even close relatives by differentially regulating genes involved in metabolite exudation and transport processes, making the study of microbial transporters a compelling topic for future studies. Thus, metabolite uptake, release, and sensing are important factors in shaping microbial communities. Metabolite turnover in soil is influenced not only by plants, but also by functionally diverse bacteria, fungi, and animals. Plant–fungal and plant–animal interactions in the rhizosphere go beyond the scope of this review, and are discussed elsewhere. Here, we provide a few brief examples focusing on the impacts of mycorrhiza on rhizobiomes and exometabolite turnover. Endomycorrhizal fungi receive a significant fraction of the carbon fixed by plants . Interestingly, these fungi also exude sugars, shaping a distinct bacterial community. Likewise, Ectomycorrhiza receive carbon from plants, and form a dynamic bacterial community; they even participate in plant to plant carbon transport. The field of fungal microbiomes is nascent: if and how fungi control exudation, whether fungal microbiomes have beneficial functions, and how plant and fungal microbiomes influence each other are all unknowns. Although many questions remain, these recent findings already suggest that a holistic view of rhizosphere nutrient cycling and signaling exchange via exometabolites requires a whole community approach including all domains of life.Plant exudates shape microbial communities. Overall, plants exude up to 20% of fixed carbon and 15% of nitrogen, which includes an array of simple molecules, such as sugars, organic acids, and secondary metabolites, as well as complex polymers, such as mucilage . Although every plant produces exudates, the amount and composition of root exudates varies. First, exudation is defined by the genotype of the host, as observed in the distinct exudation patterns of 19 arabidopsis accessions. Strikingly, the amount of variation between the accessions depended on the metabolite class investigated. Glucosinolates displayed most, flavonoids medium, and phenylpropanoids low variability. Second, exudation changes with plant developmental stage: with increasing age, arabidopsis sugar exudation decreased, and amino acid and phenolic exudation increased. Third, exudation is modulated by abiotic stresses: the amounts of exuded amino acids, sugars, and organic acids changed in maize grown in phosphate , iron , nitrogen , or potassium deficient conditions. In addition, phosphate deficient arabidopsis plants increased coumarin and oligolignol exudation, heavy metal treated poplar induced organic acid exudation, and zinc deficient wheat increased phytosiderophore exudation. Differential exudation is a plausible mechanism by which plants could modulate their interaction with microbes, as exemplified by the correlation between exudation patterns and rhizobiome variation reported for eight arabidopsis accessions. Differential exudation modulated by transport proteins is discussed below.Plant derived exometabolites need to cross at least one membrane to transit from the cytoplasm of root cells into the rhizosphere. There is considerable discussion as to what degree plants are able to regulate this transport. In general, different modes of transport could be envisioned. First, small, hydrophilic compounds could diffuse from the root into the rhizosphere, driven by the large concentration gradient. Second, channel proteins could facilitate such diffusion. Third, active or secondary active transporters could shuttle compounds across membranes against a concentration gradient. Diffusion of compounds can only be relevant in young root tissue, which is still devoid of Casparian strips or suberized endodermis that both block apoplasmic flow in adult tissues. Transport proteins involved in exudation are mostly elusive. From a conceptual point of view, plasma membrane localized exporters likely have a direct, and vacuolar transporters an indirect effect on exudation. The vacuole is a major storage organelle for many metabolites detected in exudates, such as sugars, organic acids, and secondary metabolites. Alteration of vacuolar transporter levels impacts vacuolar and cytosolic concentrations and, thus, can influence metabolite exudation into the rhizosphere. The few characterized transporters involved in exudation are essential for the transport of specific compounds, and are presented in Table 1. Since only a few transporters involved in exudation have been characterized, we suggest additional families that might be involved in the process. To complete the picture of metabolite exchange between roots and soil, Table 1 additionally contains a few important plasma membrane localized metabolite uptake systems. Below, we discuss the evidence for transport processes involved in the import and exudation of compounds detected in root exudates, such as sugars, organic acids, and secondary metabolites.

Multimedia models for ENMs can predict environmental concentrations based on sources of continuous, time dependent, or episodic releases and are similar to multimedia models that predict environmental concentrations of organic chemicals and particle associated organic chemicals.For ENMs, predicting particle size distribution as affected by particle dissolution, agglomeration, and settling is desired for various spatial and temporal end points. For one integrated MFA and multimedia model , user defined inputs are flexible around product use and ENM release throughout material life cycles.It is noted that although validation of multimedia models is a formidable task, various components of such models have been validated as well as model predictions with such models for particle bound pollutants. Most far field models of ENMs have major challenges. First, the quantities and types of ENMs being manufactured are unknown to the general public due to issues surrounding confidential business information, leading to a reliance on market research.The resulting public uncertainty will persist while nanotechnology continues a course of rapid innovation, as is typical of new industries.The rates of product use and ENM releases at all life cycle stages are also not defined.There are challenges associated with modeling transport processes through specific media and across media , highly divergent time scales of processes, lack of required input parameters, and the need for validation of results .Several multimedia models developed for conventional chemicals could be adapted around ENMs,vertical grow but few account for fate processes specific to nanoparticles .In addition, various transport models for a single medium and in the multimedia environment could be adapted for far field analysis of ENMs, but few account for fate processes distinctive to ENMs .

Moreover, their validation, which would require ENM monitoring data, is a major challenge. The lack of understanding of many fundamental ENM behaviors under environmental conditions propagates into broad uncertainties, for example in predicting ENM removal to solids or aqueous fractions in WWTPs.ENM surface chemistries fundamentally affect ENM agglomeration or dispersion and likely affect bio availabilty.Some species on ENM surfaces may degrade in the environment,while other adsorbates can be acquired.Carbonaceous ENMs may be transformed or degraded by environmental processes such as photo,enzymatic,chemical,and bio degradation.Redox and other environmental conditions will affect nanomaterial surfaces, which for nano Ag includes formation of sulfide that inhibits dissolution.Surface chemistry also affects transformation rates of primary particles and aggregates .For many ENMs such as nanoceria,reactivity is highly size dependent. To accurately model material fates thus requires understanding how material surface properties affect integrity, how both change under varying environmental conditions such as pH, clay content,and organic matter content, and how surface properties and particle reactivity affect physicochemical processes that are parametrized in far field models. This is especially true for ENMs used as pesticide delivery mechanisms, including carbon nanotube composites with specifically reactive surface monomers. Yet only recently has modeling attempted to address differing properties of a material’s structural variants .Evaluating computational model predictions is a challenge for ENMs, which presently are estimated to occur in the environment at low concentrations.Also, detection methods for ENMs in environmental media and distinguishing ENMs from natural chemical analogs are still under development,with more evaluation strategies needed including a framework for validating new ENM analytical detection methods.

Fullerenes from incidental sources were quantified in river sediments collected from locations across the globe and quantified in the atmosphere over the Mediterranean Sea.Perhaps related to a viable exposure scenario, fullerenes were quantified at relatively high concentrations in treated wastewater effluent and at ng/L to μg/L concentrations in river waters receiving effluent discharge. While not necessarily nanoscale, similarly high concentrations of TiO2 were reported for sediments sampled near a WWTP outfall.The greatest uncertainty in ENM exposures is near field , at the receptor where toxicant dose manifests as internal dose. Heteroaggregation is a dominant fate process for ENMs when they interact with natural colloids.Given sufficient residence time for ENMs in environmental matrices, heteroaggregation and to a lesser degree homoaggregation will affect localized compartmentalization, including stability in the water column and therefore, sedimentation.However, these processes do not preclude biological impacts under simulated environmental conditions, as has been shown for nanoceria in a complex aquatic mesocosm.Exposure can be confirmed by quantifying receptor body burdens, thereby allowing for quantitatively relating near field exposure to biological effects.Thus, in the absence of detailed, biologically complex, near field models for local exposures to environmental receptors, the ability to trace ENMs to biological receptors sampled directly from the environment becomes the best available approach to relate far field exposures to biological impacts.Overall, material flow models and multimedia modeling of ENMs have advanced to inform ENM ecotoxicology. Available far field modeling frameworks are adaptable to changing inputs despite uncertainties in production volumes. Major uncertainties remain at the nexus of ENM surface and core chemistries as related to nanomaterial transport, aggregation, and degradation characteristics.

However, fundamental research is needed to discover and parametrize complex fate processes. New approaches, such as assays that can be used to rapidly probe surface associations,demonstrate how to populate far field models and how to determine near field exposures associated with effects. Although existing models can simulate particle movement, deposition, and some transformations, the knowledge state regarding ENM environmental exposure conditions via measurements or modeling simulations cannot be assumed to accurately represent actual conditions at biological receptors.Many of the outstanding research issues and recommendations for evolving ENM ecotoxicology are echoed in the discourse for other chemicals of emerging concern .These include the need for systematically understanding ENM and decomposition product toxicity across various receptors within linked levels of biological organization,quantifying actual exposures and uptake into environmental receptors,gaining mechanistic insights into and biological markers for acute and chronic low level exposures,and understanding how environmental factors including cocontaminants affect ENM transformation and biological impacts. Still, how can the potential for exposure and impacts of ENMs be anticipated, prevented, managed, or mitigated? Further, what data and tools do decision makers need to inform their work? While no formalized process for incorporating all exposure conditions and concepts of ENM transformation, dose, and body burden into risk assessments currently exists, a proposed framework approach to risk characterization over the life cycle of ENMs has been published and is available.This framework advocates an initial decision cutoff in regards to exposure; in the absence of exposure,indoor growers the need for further assessment is diminished or negated.In this available framework, ENMs that are certain to rapidly dissolve into ionic components in a destined environmental compartment would be assessed for risk based on the released components rather than the original nanoparticles.Persistent ENMs are expected to accumulate in matrices such as sediments.The consequences of ENMs to successive generations, biodiversity, and ecosystem services are not addressed by model organism specific assays of discrete growth and mortality.Nonetheless, in this available framework, toxicity end points associated with standardized testing protocols for sediment, aquatic, and terrestrial standard population level end points over short and long time frames are advocated for assessing hazards of simulated ENM concentrations in the environment.In this framework, sunlight is an environmental variable, bio accumulation is measured, and ENM modifications during product and material life cycles that may change bio availability are considered.While such a framework has broad organizational appeal, priority setting within the framework is required and thus could focus on tests that are relatively well aligned with likely exposure scenarios. Even with a risk assessment framework that considers ENMs across product life cycles and considers sediments, water, and soil in testing end points,major hurdles hinder regulatory agencies, and research scientists, in using concepts such as exposure conditions, ENM transformation, dose, and body burden in interpreting biological and computational findings for assessing risks. Toxicity tests developed for dissolved chemicals typically require significant modification for use with ENMs.Tests may not apply to ENMs if they are not appropriate for solids.Additional scientifically based hazard information from the peer reviewed literature may or may not be available for consideration. ENMs used in ecotoxicity tests, which are sometimes laboratory synthesized to overcome uncertainty regarding proprietary coating or other commercial formulations, may be insufficiently analogous to allow for extrapolating information or risk comparisons.

Issues include the need to know test material characteristics and how they relate to testing results and the ENM life cycle. Even if an initial risk assessment considers ENM solubility,ENM dissolution is not instantaneous; therefore, at what stage of dissolution does the contaminant no longer pose a hazard as an ENM? Also, where biological impacts stem from ENM surface characteristics, how can mass concentration be used to judge hazards? Environmental ENM effects in benchtop experiments can be indirect, stemming from physical nutrient depletion,or amplifying organism uptake of cocontaminants.Other indirect physical effects derive from ENMs adhering to the organism surface,light shading,or internal food displacement.Near field exposures can result in biological hazards from specific ENMs based on their properties .By definition, ecological risk assessment is “the process for evaluating how likely the environment will be impacted as a result of exposure to one or more environmental stressors.”ERA involves predicting effects for individuals, populations, communities and ecosystems, and concerns itself with valuable ecosystem services such as nutrient cycling.Thus, conducting ERAs for ENMs could benefit from an ecological outlook. All levels of biological organization, and interactions between them, would be considered when assessing responses to ENM exposure . Release and exposure scenarios , use of functional assays for assessing environmental compartmentalization ,and combined life cycle and multimedia modeling have important roles in focusing ENM ecotoxicology. Less recognized is that mechanistically based models of dynamic biological effects are informed by hazard assessment research. Different types of process based, dynamic models allow for predicting effects from exposures stepwise, starting at sub cellular levels, into individuals, through populations, and conceivably to communities and ecosystems. Developing process based models requires researching key effects processes and ecological feedbacks.Models are formalized to describe interactive processes culminating in toxicity such as reactive oxygen species generation and cellular damage. Process based mathematical expressions evolve with empirically based discoveries or through model reconciliation with experimental data. Parameters are independent of toxicity testing protocols, although models could be informed by standard test results. Thus, ENM ecotoxicity research could support predictive toxicology by informing and populating process based, dynamic ecological effects models. A comprehensive fate and effects research agenda is needed for addressing ENM quantification in complex media.Such an agenda has allowed for assessing experimental compartmentalization,and sensitively assessing environmental persistence,toxicity, bio accumulation,trophic transfer,and indirect effects from the uptake of ENMs coated in other hazardous materials.Such research could substantially inform ENM risk assessment for a relevant environmental exposure scenario. However, most ENMs have not been studied comprehensively along the entire exposure and effects continuum . Further, the approach is not sustainable. Rather, the need is to develop efficient approaches applicable within an overall approach to rapidly evaluate the large number of ENMs under commercialization . A research agenda that focuses on distilling key determinants of exposure and hazard for ENM environment systems that can be measured experimentally would be most compelling. Thus, while the science of ENM ecotoxicology and exposure characterization has advanced, there are disconnects between how regulators review ENM based products for environmental safety and the research that is conducted to evaluate hazards. Except for results published in open source outlets or directly reported, research may be unknown to government bodies. Ongoing synthesis of published research results is challenging due to high variability across study conditions and ENMs tested, and due to effort needed to regularly update such comparisons. Moreover, there is a systematic resistance to publishing “no effect” studies in the peer reviewed literature.As a result, relying only on published research to inform regulatory decisions can present challenges. A life cycle based framework facilitates exposure modeling and hazard testing to support risk assessment. However, extrapolation of effects to untested concentrations, study, or environmental conditions, and across biological levels of organization, requires understanding dynamic biological process based effects, which current standard tests neither deliver nor sufficiently inform. Ultimately, exposure scenarios are useful for framing and focusing ENM ecotoxicology, and some version of a tiered intelligent testing and risk assessment strategy is needed. Such a conceptual tiered strategy considering the impact of the ENMs’ varying properties on ecological risks at different life cycle stages was proposed in the EU FP7MARINA project and is being further developed in the EU NANoREG program.

On the strength of these narratives, they can cultivate support at home for laws of return or flexible citizenship regimes, or seek support abroad from diaspora nationalist communities. It is not a given that these stories will be accepted or acted upon, but it is clear that sometimes they are, to dramatic effect. When differentiating between transnational practices undertaken for purely practical economic interests and those undertaken for religious, ethnic, or identity-based reasons becomes difficult, it becomes yet more important to recognize how the reality of diaspora and the myth of diaspora can be used to move people, money, and ideas in ways that simple labor forces never could. Following S, person after person told me similar things about their fear and dislike of their future Arab neighbors, and a few also told me that they would prefer to live outside of the increasingly Latino neighborhoods springing up in Beersheba, Ramla, and Tel Aviv. How did my subjects learn about the Israeli/Palestinian conflict, and how did they learn to place themselves so firmly against the Arab side of it? Why are they all ending up in Ramla anyway? Why in the world should their fellow Latin American Jews be lumped in with Palestinians as people to avoid once they make aliyah? And what does their curious, tenuous position tell us about the way race and immigration operate in Israel? Obviously, people exist outside and beyond this divide; the binary is only a politically expedient assumption. Even within the Jewish “side,” perceived race is predicated on a complicated and nuanced set of associations between different Jewish groups, affected by skin color, religious practice, language, and former national origin, among other aspects. Iquiteño Jews fall firmly on the Jewish side of that foundational split,stackable planters but they fit uncomfortably within that side. In this strange position, they highlight a fundamental Israeli paradox.

Secular nationalists in Israel need Jews to outnumber Palestinians within its territory, and so Israel constantly desires new Jewish bodies. To get them, it broadcasts a welcoming face to the diaspora, encouraging immigration under the Law of Return. This desire, however, must contend with powerful ultra-Orthodox gatekeepers that disapprove of conversion into any kind of non-Orthodox Judaism, and with the racism of other secular-nationalist Israeli Jews.However, they are not Jewish in the right or the most desirable ways. As they make their way to Israel, they must jump through administrative and religious hoops to please both sides, and along they way, they form their own opinions about their identities, Israeli racial hierarchies, and Jewishness itself. The case of Iquiteño Jewish migration is proportionally tiny, but it handily reveals Israel’s tenuous balancing act between secular-nationalist and ultra-Orthodox politics, and highlights the fragility and arbitrariness of the definition of Jewishness that Israel relies upon. Howard Winant and Michael Omi’s definition of a racial project is useful in discussing the creation of Israel’s racial system. A racial project is “is simultaneously an interpretation, representation, or explanation of racial identities and meanings, and an effort to organize and distribute resources along particular racial lines”. Omi and Winant often fail to see the ways in which religion becomes racialized, or the overlap between religion and ethnicity , unfortunately. Such an intersection is easy enough to fill in after the fact, particularly with the help of the clear example laid out before Iquitos. The state of Israel knowingly and actively pursues a racial project that privileges Ashkenazi religious and cultural behavior alongside phenotypical representations of race. In order to bridge this gap, I use Orna Sasson Levy’s work to describe how sub-ethnic differences within the Jewish population rub up against racial differences, as well as Yehouda Shenhav’s discussion of “Arab Jews” , which complicates the assumed simplicity of the Israeli/Palestinian divide. The end result is a racial project that hides the real complications of identity in Israel from vital prospective citizens.

Israel’s multi-part racial hierarchy privileges an ideal Jew who is pale-skinned, descended from European Jewish immigrants, observant and Orthodox enough for civil benefits but not too Orthodox18, and Ashkenazi in practice and culture. For those of Israel’s Jewish population who do not fit this mold, a complex hierarchy exists between different Jewish groups, forming a two part intra-Jewish racial structure where both perceived race and Jewish sub-ethnicity can be vectors of privilege and oppression. These groups may combine ethnoreligious subcategories and racial identities in a number of ways; however, almost all of them strive to be read as not Arab. Non-Arab, non-Muslim, non-Jewish peoples with a long history in Israel, such as Armenian Christians, are marginalized civically and politically , and do not figure largely in the racial imaginations of most Israelis. Newer non-Jewish, non-Arab immigrants have also been drawn to modern Israel, including a population of Catholic Latin Americans. They too are a very small minority and are generally excluded from discussions of racial formation and hierarchy within the country. Considering these elisions, the most basic division of Israeli society is thus between Jews of any race or ethnicity and Palestinians. Israel’s situation is quite different from American racial projects, which are perhaps its closest cousins, and I do not wish to ignore these differences or apply American racial optics carelessly. Israel’s history, its theological governance, and its demographics are very different, as are its modes of thinking about race, citizenship, and belonging. That being said, some models of race developed in the United States, when adapted, can shed light on other cases. In Israel specifically,stackable flower pots bringing in such theories is useful because countries wrestle with a popularly assumed racial binary that hides much diversity. When used alongside scholarship like that of Sasson-Levy and Shenhav, the existence of the imagined but strict Israeli/Palestinian binary leads to fruitful theoretical comparisons. In particular, I find that this system in some ways resembles Claire Jean Kim’s U.S.-based theory of racial triangulation. 

Kim theorizes the racialization of Asian-Americans within the American “field of racial positions” as a process that does not happen in a vacuum in which each ethnoracial group receives particular treatment independent of the treatment of other groups, nor in a strict hierarchy bounded by Black and White, but “relative to and through interaction with” all groups. These fields of racial positions acknowledge the power of public discourse, personal interactions, and structural forces in shaping the relative privilege of racial groups in a shifting arena specific to time and place. This form of racialization allows for multiple axes of racial formation and foregrounds the manner in which different groups are racialized through comparisons with others. When she argues that Asian-Americans are “racially triangulated” within these fields, she illuminates the ways in which Asian-Americans define themselves and are defined by others in contrast to White and Black Americans through processes of relative valorization and social ostracism. By borrowing Kim’s vocabulary to refer to Israel, I locate Iquiteño-Jewish migrants within a field of racial positions that includes Palestinians, non-Jewish and non-Arab migrants, and multiple subgroups of Jews with varying levels of ethnic and religious privilege. Their identity is triangulated in relation to, especially, light-skinned Ashkenazi Jewish Israelis and Palestinians. Iquiteño Jews, mostly, are converts in the Conservative/Masorti movement, people with dark skin, people with Sephardi rather than Ashkenazi heritage, second- or third-language speakers of Hebrew, and recent migrants. As such, they are racially constructed through social ostracism when compared to light-skinned Jewish Israelis, European-descended Ashkenazim, first-language speakers of Hebrew, those born in Israel, and Orthodox Jews, among other axes of identity. Legally, as non-Orthodox Jews, they have fewer dejure rights in Israel, such as to marriage. Socially, they face colorism, language discrimination, anti-immigrant bias, and anti convert bias. At the same time, they enjoy innumerably more rights, both de facto and de jure, than Israel’s Palestinian citizens. How aware of this situation are the Jews of Iquitos? It is not clear to me or to my subjects how legible Iquiteños moving through Israel are as non-Arab, or even perhaps non-Christian. However, it is clear that in Iquitos, potential olim know enough about Israeli racial hierarchies to name themselves as emphatically not Palestinian, and to preemptively take action to distance themselves from Palestinians. Interview subjects did so by expressing their desire to move quickly away from Ramla, which they saw as a demeaning or undesirable place to live because it had a high proportion of Arab residents. A younger female friend of S, the interviewee who opened this chapter, told me in hushed tones that she had heard Ramla was violent and unhealthy —because of its Arab population. My youngest respondent, a young man of , planned to immediately join the IDF for a variety of reasons, including the opportunity to undergo an expedited Orthodox conversion in the military, but also to “defend [Israel] from rats,” meaning displaced Palestinian families who might wish to return to their ancestral homes. My hosts appeared generally moderate in their Peruvian political opinions, and were by and large vehemently anti-Trump, but when I asked them who they would vote for in the then-upcoming Israeli prime ministerial election, they responded that they liked and approved of the Likud party’s policies around checkpoints and the building of new settlements.

Clearly, many Iquiteño Jews felt a deep anxiety about Palestinians in Israel. Those who did not involve themselves politically were nonetheless entering a situation in which their presence would inherently help the Israeli state disenfranchise Palestinians with equanimity. At the same time, my respondents divulged much less anxiety to me about their position within the intra-Jewish Israeli hierarchy. Although in 2019, three individuals informed me that Ramla was undesirable not only because of the large Arab population but also because they felt other Latin American Jews were broadly undesirable to be identified with, few others expressed such sentiments. While many told me they felt anxious about learning and using Hebrew on a daily basis, introducing their children to such a new place, or finding good work, it seemed to me that most felt excited about merging into a Jewish-Israeli whole, deeming such assimilation entirely possible. It was not clear to me in any instance in my 2019 interviews that individuals felt they “should” be more identified with either Ashkenazi or Sephardi Jews in Israel, or that there was much trouble with racism within the Jewish population in Israel. Some older respondents, particularly when I spoke to community elders whose families had maintained Judaism through the Iquitos community’s lean years in the late 20th century, mentioned that they strongly identified as Loretano Jews, who had a practice and history all their own, but that identification waned quickly as respondents grew younger. Those who felt those ties to a Peruvian, non Ashkenazi form of Jewishness were also much less likely to report a desire to migrate or a sense of already being Israeli, rather than or in addition to being Peruvian. This provides a picture of Jews who feel themselves already comfortably ensconced within a privileged majority. That said, I do find it interesting and important that even three of my respondents would feel the need to preemptively distance themselves from other Jewish Latin Americans living in Israel. It is even more interesting that not a single person I spoke to was interested in reclaiming the traditions of their Moroccan-Jewish ancestors, or connecting with Moroccan-Jewish communities within Israel. The current community leaders had not considered reaching out to the Sephardi Chief Rabbinate for assistance or educational materials, content with the Ashkenazi-normative materials and training sent by such organizations as the Jewish Agency for Israel. However roundabout the way, and however quiet the transmission, clearly some Iquiteños are receiving some information that allows them to preemptively triangulate themselves before making aliya. Information that comes to Iquitos about racialization in Israel comes from Iquiteño Jewish family members and friends living in Israel, the Spanish-language Jewish news media, rare features in the general Peruvian press dealing with Israeli issues, Jewish organizations interacting directly with Iquiteños, and visitors. Notably, most of the Iquiteño Jews could not name a favored Israeli party or politician when I asked them to. 

In the case of Iquitos, why do people simply not respond to Mormon or Evangelical Christian overtures? The community, its actions, and the relationships converts build with each other are key not only to why individuals convert, but can explain how new converts are brought into the fold. In the field of pastoral psychology, Ines Jindra combines two important concepts in the service of studying conversion: critical realism and the toolkit approach8. Critical realism allows for multiple levels of truth, which Jindra characterizes as what really happened and what actually happened. This allows personal conversion narratives to be important and truthful while also acknowledging other forces that may push someone towards conversion. It goes some way to healing the problem Gauri Viswanathan sees in the sociological study of conversion, where personal narrative and the power of belief are disregarded. The toolkit approach, meanwhile, draws on cultural studies to recast religion as a tool with many uses, both spiritual and practical. In this way, granting religion validity as a tool means that transformation, where there is a change in a person’s values, outlook, and sense of self, among other key characteristics, and conversion, a change from one religion to another, do not march in lockstep. Yang and Abel, while they intend to characterize the sub-field of sociology that focuses on conversion, also lay out a three-tiered model from which they say sociologists pick and choose influences. I intend to use this model more intentionally, where the tiers are like baskets from which certain influences are more salient, and which the convert responds to with their religion, as in toolkit theory. The three levels, or baskets, are the macro,aeroponic tower garden system the meso, and the micro level. The macro has to do with very broad-scale forces, such as globalization or transnationalism, that change a person’s societal surroundings.

This could connect to Lofland and Stark’s predisposing conditions. The meso could also be called the institutional level; it is where congregations, community and activist organizations, and even large international NGOs are found. This level is critical to the supply side Phillips and Snow identify; these are the institutions that shape what affective bonds and intensive interaction can look like for a particular community. Finally, the micro level is where individual narratives of spiritual seeking, feelings of belonging, or personal troubles can shape decisions to convert. I have chosen not to copy these levels exactly but to adapt them, combining the individual and the immediate religious community, seeing the international arena of individual states as the middle level, and taking in the grand networks of transnational activity as the largest scale. In understanding conversion in Iquitos, then, I draw from each of these models. In particular, the focus on community, the recognition that religious communities are affected by strong political forces, and the connection between the individual and the world are key. Drawing from Yang and Abel’s leveling technique, the various factors can be described as follows. At the global level, individuals a macroeconomic and political situation that makes migration from Peru to Israel more attractive in general, and a transnational social field made possible by global advances in transport and communications technology. The Iquitos case is interesting on itsmerits, and it also helps us understand that the usual sociological division between practical and religious motivations for conversion is flawed, and that any focus on conversion as purely instrumentalist or purely a subject for the spirit is necessarily incomplete. It is obvious that religion and worldly concerns influence each other, but when it comes to conversion, sometimes worldly concerns are religious and vice-versa.

Furthermore, Iquitos helps us understand how narratives and myths of diaspora can actively drive practical transnational movement in the modern age by creating new forms of religious authenticity linked to politics, place, and movement. At the state level, major Jewish institutions like the Jewish Agency operating in Latin America are interested in potentially supporting an isolated community with a complex history are primarily Ashkenazi, usually quite large, and often connected with the State of Israel. In Israel, the Law of Return’s current iteration requires certain bonafides from potential immigrants. Together, these forces have helped shaped what conversion, and therefore Jewishness, looks like in Iquitos. Finally, at the individual/community level, individual Iquiteños interpret and respond to the institutions and options available to them using all the tools in their kit, including religious ones, which are in turn influenced by the two broader levels. By the end of this chapter, I wish to demonstrate that the Latin American-Jewish institutional resources available to the Iquitos community early on shaped an orientation towards Israel. That early orientation combined with the economic situation of Iquitos led to an early wave of migration. Those first migrants established what would become a transnational social field between Israel and Iquitos. The template for Jewish education and conversion continued combined with contact between Iquiteños in Israel and Peru led to a blending of Jewishness and Israeliness in the Iquiteño imagination and also provided more standard pull factors for further migration, resulting in state appropriation of diasporic identity to drive today’s migration patterns.Traces of Iquitos’ historical Jewish presence jump out from between the saints’-name streets, the churches and monasteries, and Jesus-bedecked public buses with surprising ease. The large supermarket in the historic city center does business in the old Casa Cohen, its sign still hanging above the portales that give the current store its name. On the same street is the current synagogue,dutch bucket for sale hidden behind a mattress and fabric shop.

One of the ubiquitous mototaxis coughs by with a phone number and an elaborately calligraphed surname that immediately surprises me with its almost humorous Jewishness — I later hear from an interview subject who shares the same apellido that the owner-driver is a distant cousin from the branch of the family that did not hold onto or return to their Jewish ancestry. Iquitos’ most famous living artist is the ironically named Christian Bendayán, descendant of second-generation patriarch León Bendayán. In the municipal cemetery, a small fenced-in meadow marks the Jewish section, where flowers give way to river pebbles and red-and-black huayruro seeds placed on the headstones. Someone was buried there just two months before I arrived. Online, things look pretty good too. The Kehilá runs not one but two Facebook pages which post at least a few times a week, and the first Google search result for “Iquitos synagogue” is a helpful webpage on TurismoJudaico.com. At the time of writing, the English-language Wikipedia page returns nine results for the word “Jew,” the Spanish page five, while on Hebrew Wikipedia, the section simply called “Yehudim” is more than twice as long as the general history section. Several articles in online newspapers also come up in a Google search, from long features in The New York Times and The Guardian to Sefardi special-interest websites to Zionist RSS feeds to local Spanish-language dailies. Most of them have been written since 2010, when The Fire Within, a 2008 documentary directed by Lorry Salcedo Mitrani about the community’s renaissance, made the film festival circuit. All this despite the fact that the most common response to my research wherever I go is an incredulous, “There are Jews in Peru?” Sitting in the courtyard of the synagogue, conducting my scheduled interviews and also swooping down on unsuspecting visitors who drop by for coffee, help with Israeli immigration documents, and sometimes mattresses, I get a different picture. A little girl of six who I remember as a toddler from my last visit tells me in passing that she always comes to Monday “Judaism classes” because it is a chance to see her same-age friends, who, she sighs, will all be leaving soon except for her. Of all my interview subjects in 2019, only that girl’s father and two others tell me they intend to stay in Iquitos with their families to keep the Abramowitzes company. Over coffee on day one of my 2019 visit, Jorge Abramovitz, the de facto leader of the community and owner of the synagogue building, tells me something Ryan Schuessler quoted him on in The Guardian in 20169: “La comunidad puede morir.” The community may die. The sentiment is independently repeated to me by Señor Abramowitz’s wife, several of my interview subjects, and the little girl, who appoints herself my unofficial guide after I spend at least an hour with her lying on our fronts trying to make nice with the mattress shop’s resident ice queen cat. The presidents expect that no more than five to seven families of the twenty or so presently there will remain — some will have to stay whether they want to or not due to family matters or money troubles.

What can explain the gap between the international perspective on Iquitos and the reality that the community once more appears to be going dormant, if not dying?Migration is an intrinsic part of broader processes of development, social transformation, inequality, and globalization. The relation between migration and inequality is complex and fundamentally non-linear, but there is a strong relationship between economic development and migration. It is generally assumed that when moderately high inequality and an international arena that encourages some movement exist in conjunction, an integrated migration system exists. As of 2018, Peru’s GNI per capita was 6,530 USD, while Israel’s was 40,850 USD, a clear difference, although as of 2016, both countries’ GINI index score was only 4.6 measures apart. Generally, middle-income countries like Peru have the highest emigration rates because of a combination of relative deprivation and tighter links to developed countries — in Iquitos, this link is the somewhat nonstandard link between Israel and the global Jewish diaspora.Israel, despite a sometimes difficult relationship with its diaspora , has for decades engaged in aggressive outreach to Jewish populations across the world. This includes legal provisions such as the Law of Return, which guarantees access to Israeli citizenship for migrants who meet state-determined baseline criteria of Jewish practice and/or ancestry. Accessing the benefits of this law often requires that potential migrants be able to provide documents such as parents’ Jewish marriage certificate , burial records, and/or documentation proving conversion. Since the 1970s, the Israeli state has in general encouraged both migration and conversion in order to boost the absolute numbers of Jews in the country, although this has deepened struggles between secular Zionists and ultra Orthodox religious Jews in the state apparatus, and led to ambiguous or difficult situations when groups cannot provide such documentation, claim Jewish identity, and do not convert. NGOs like the Jewish Agency for Israel and the Jewish National Fund conduct outreach between Israel and other countries, while organizations at the national level, like the Federación Sionista del Perú, engage in Israel-positive activities for a local or regional audience. Conceiving of Israel as the natural center of Jewish life, practical or religious, is a relatively recent phenomenon: indeed, for most of Rabbinic Jewish history, the land that was to become Israel was a backwater that maintained a symbolic, ritual importance rather than being a practical goal for most Jews. As will be discussed in the next chapter, that the modern state of Israel today seems a natural point of interest for Jewish migrants across the globe is evidence of a successful parlaying of a symbolic diaspora, which was in reality only loosely connected between its individual nodes, into practical transnational activity, including migration, money flow, and idea exchange. Altogether, it seems evident that migration was a response to circumstances that any Iquiteño person might have chosen. This simple model does not explain, however, why Israel? Why not Lima, the center of Jewish life within Peru? Beyond internal migration, why not the U.S., Spain, or Argentina, the first, second, and third most-common host countries for migrant Peruvians ? Why go through the long and involved process of conversion , followed by the long and involved process of making aliyah? It is the history of the state and institutional history one level down from the interconnected world that helped fuse Jewish and Israeli identities in Iquitos that explains why Israel specifically became the goal.

That P. ramorum also persisted on green leaves at high levels for the entire 16 weeks despite the loss of approximately 40% of leaf biomass stands in contrast to our previous findings where its colonization of leaves peaked within a few weeks after exposure in natural streams, but then rapidly dropped to very low levels as colonization by clade 6 Phytophthora species rose and persisted at high levels. This is evidence that the reduced recovery of P. ramorum from green leaves in natural streams as decomposition progressed was due to displacement from saprotrophic organisms like clade 6 Phytophthora species. Unfortunately, P. ramorum was completely suppressed from colonizing leaves in combined inoculations with P. gonapodyides and it could not be determined if the pattern observed in field experiments would occur under these simulations when both species were present. The suppression of P. ramorum colonization of green leaves in combined Phytophthora inoculations—consistent across all three experiments—was surprising because both species were effective at colonizing leaves when inoculated alone. One explanation could be that sporulation of P. gonapodyides from mycelial mats occurred earlier than that of P. ramorum and that the latter was therefore precluded from leaves because in all experiments, full colonization of green leaves by P. gonapodyides occurred very rapidly. Indeed, in the first experiment, colonization of P. gonapodyides occurred more rapidly on green leaves than that of P. ramorum. However, baiting two days after inoculation in the second experiment showed that P. ramorum spores wereactive in the microcosms where it was inoculated alone,dutch bucket hydroponic but almost absent in the combined inoculation microcosms. This suggests that the presence of P. gonapodyides itself may have suppressed sporulation by P. ramorum. The rapid leaf colonization by P. gonapodyides in these microcosms also contrasts with the slower colonization that was observed in natural streams and may be an artifact of high inoculum loads and the relative abundance of substrate.

The aim of these experiments was to characterize the capacity of each organism for growing and reproducing from each type of leaf rather than estimating typical colonization and decomposition in streams. Though logistically more difficult to prepare and standardize for an experiment of this magnitude, using sporangia or zoospore inoculum rather than mycelial mats may overcome the problem of uneven inoculum activation, the success of which we have experienced in smaller scale experiments. Alternatively, the use of colonized plant tissue instead of mycelial mats as a source of inoculum may also produce a different outcome from the suppression of P. ramorum that we found with this approach in mixed inoculations. Interestingly, the kind of succession observed in field experiments did occur in a few control microcosms into which both Phytophthora species were accidentally contaminated. However, the limited occurrence and unknown relative quantity of original inoculum precluded more substantial evaluation. In any case, the suppression of P. ramorum sporulation in treatments where P. gonapodyides was present raises the question of what mechanism was responsible for the effect. It also furthers the impression that P. gonapodyides and other clade 6 Phytophthora species may have a moderating effect on the presence of P. ramorum in streams. The green leaves that we used were of mature cuticle and collected in midwinter and late summer for the first and second experiments, respectively. While some seasonal variation in susceptibility to P. ramorum infection has been reported in California bay leaves, the physical and chemical properties of mature leaves have also been reported to be relatively consistent throughout the year. Our results were similar for both experiments, and therefore, any variation in the leaves was overcome by experiment factors. The extensive colonization of brown leaves by P. gonapodyides and their limited colonization by P. ramorum is consistent with previous work where we showed that the former is a competent saprotroph while the latter is relatively ineffective at colonizing dead tissue. A significant discovery in this work was that P. ramorum colonized yellow, senescent leaves that were still fresh and had an intact cuticle to nearly the same degree as it did green leaves.

At this stage, though chloroplasts and most of the protein content are gone from leaves, the cells are expected to be still alive, while in brown leaves that have dried the cells are no longer biologically active. In fact, colonization of the yellow leaves by P. ramorum was not quite as extensive as its colonization of green leaves in the second experiment, which ran more or less concurrently and in which green and brown leaves were maintained in separate microcosms , though the difference between the separate experiments was not analyzed statistically. Though green leaves are shed into streams as a relatively low proportion of total litter, yellow leaves, often shed directly into streams from trees, constitute a much greater proportion of leaf litter in streams. This indicates that a great proportion of leaf litter in the streams is suitable for colonization by P. ramorum, and conforms to the regular recovery of this pathogen from natural leaf litter. Furthermore, the degree of colonization of yellow leaves by both Phytophthora species remained persistent throughout the 16 weeks, as with green leaves in the other experiments, suggesting that the same kind of succession may be expected in these leaves as seen with green leaves in natural streams. Also consistent with previous findings with leaves colonized in naturally infested streams, leaves colonized by both Phytophthora species were generally conducive to sporulation as detected by baiting from the microcosms. Phytophthora gonapodyides was consistently recovered from P. gonapodyides-only and combined Phytophthora species inoculation treatments where it had colonized all green and brown leaves at all sampling points. The results from baiting of P. ramorum spores from microcosms were less regular, but nonetheless, mostly successful from microcosms containing colonized green or yellow leaves and occurred minimally from microcosms containing brown leaves which were colonized at only very low levels. The relatively less frequent recovery of P. ramorum by baiting from microcosms with non-sterilized stream water, not observed for P. gonapodyides,dutch buckets system may be the consequence of P. ramorum not being well adapted to sporulation in biologically active aquatic environments or relying on different environmental signals.

Nevertheless, these results confirm that both of these Phytophthora species can sporulate from colonized, decomposing leaves, whether green, yellow or brown leaves. Furthermore, at least under these conditions, their spores persisted for weeks and even months after any visible substrate was available, though the effect occurred more defifinitively and for longer with P. gonapodyides. As P. gonapodyides is not known to produce long-term survival structures, the question arises of how P. gonapodyides persisted so long in the microcosms in the absence of leaves. This observation also stands in contrast to our successful elimination of Phytophthora spores from original stream water collections simply by holding the water at cool temperatures for approximately three weeks. The observed persistence of spores of both Phytophthora species may be the result of an abundance of zoospore cysts due to the compact nature of the microcosms, or perhaps because the spores originated from propagules that would not have been suspended in the water column of the flowing streams. While oomycetes have been acknowledged as decomposers in aquatic environments until recently they have primarily been regarded as acting on non-cellulosic detritus such as insect and animal tissue. As most Phytophthora species are known as plant pathogens, the recent evidence that they may also degrade plant tissue in detritus is not surprising. Parasitism is considered an early characteristic in the evolution of oomycetes, but the possible evolution of a saprotrophic lifestyle from parasitic precursors has been considered for fungi and oomycetes.Stradling saprotrophic and parasitic lifestyles, stream-resident Phytophthora may play an important role in the early breakdown of leaves and vegetative matter that still contain living cells. As facultative pathogens, clade 6 Phytophthora species can enter living cells and open intact tissues to further colonization by other saprotrophic organisms with less ability to penetrate living tissue. This is analogous to the paradigm of ‘conditioning’ of vegetative litter by pioneer microbial species, though in this case with respect to secondary saprotrophic microorganisms that could not on their own overcome physical and chemical protections still present in senescent but still alive leaf tissue. Our results were consistent with this hypothesis, as green leaves decayed more slowly in the absence of Phytophthora. It is uncertain why in the first experiment green leaves in the treatments with no Phytophthora inoculation decomposed very little over the entire 16 weeks of the experiment. In this experiment, both green and brown leaves were maintained together in microcosms, and it is possible that leachate from the leaves, particularly the brown leaves, may have had an inhibitory effect on some microorganisms. In the second experiment, leaves were leached prior to being deployed in the experiment, and also green and brown leaves were kept in separate microcosms. Green leaves in non-inoculated controls in the second experiment lost biomass to a degree ultimately similar to that of inoculated treatments, albeit at a slower rate. This indicates that other organisms were present that could initiate the decomposition of green leaves through the presence of Phytophthora accelerated it.

We attempted additional isolations from some samples of leaves on acidified potato dextrose agar medium and found that the leaves in both controls and inoculated treatments were generally well colonized by a multitude of fungi. The fact that similar fungi occurred on leaves from microcosms prepared with both sterile and non-sterilized stream water suggests that many of these fungi were present on the leaves before entering streams as leaf litter.Additionally, overall there were no differences in decomposition rates between treatments with sterile or non-sterilized stream water added. Decomposition was also similar for leaves colonized by either Phytophthora species, indicating that, though P. gonapodyides is a better adapted saprotroph, both species had a similar effect on the decomposition of live, green and yellow leaves. This would be consistent with Phytophthora having the effect of opening integral tissue to colonization by other saprotrophs that then push decomposition forward. Finally, it is interesting that the presence of fungi in these leaves did not affect the persistence of P. ramorum throughout the experiments, suggesting that they are using different resources and that the successive displacement of P. ramorum in previous work may be specific to competition with other Phytophthora species or similar organisms. Under natural conditions, leaves would be exposed to a greater diversity of organisms, including other oomycetes such as Phytopythium species. As P. gonapodyides can colonize dead leaf tissue, it could be expected that it would contribute to leaf decay in brown leaves as well. This was not observed, as loss of biomass in brown leaves was the same in all treatments unaffected by Phytophthora colonization. The fact that P. gonapodyides substantially colonized brown, senesced leaves, but did not increase the rate of biomass loss raises the question as to what resources the organism uses in this substrate. Though biomass loss is a useful measure of decomposition, it does not offer a complete picture and other measures, such as changes in leaf toughness or chemical properties may offer a fuller picture of decomposition that could account for the effects of Phytophthora colonization. Moreover, decomposition of brown leaves proceeded more slowly in the second experiment than the first. This may be due to lower nitrogen and other nutrient availability both because in the first experiment green and brown leaves were maintained together in microcosms and also that in the second experiment, the leaves were leached prior to being introduced into microcosms at the start of the experiment. This may also be the reason that colonization of brown leaves by P. gonapodyides was significantly less than that of green leaves when leaves were kept in separate microcosms, while the levels were similar when leaves were maintained in the same microcosms. Another possibility is that sporulation from green leaves allowed greater colonization of brown leaves where the leaves were kept in the same microcosm. Our results demonstrate that green and yellow California bay leaves are suitable substrates for the growth, colonization, and sporulation of P. ramorum in streams where they constitute a significant proportion of vegetative litter, they likely play an important part of supporting the inoculum load in streams.

However, degradation product concentrations and detection frequencies were lower in the present study, likely attributable to the fact that samples were collected from homes treated with a single application of fipronil. Together, results from this and other studies indicated that dust particles exposed to fipronil may retain fipronil and its degradation products for many months after application. This suggests that urban dust may serve as a source of fiproles, especially fipronil and fipronil desulfinyl, in urban runoff long after the conclusion of pest treatment activity, barring removal or offsite transport of the dust prior to the occurrence of a runoff event. Fipronil sulfone levels gradually increased from 1 d to 153 d, with mean concentrations ranging from 1.43-209 ng g-1. Fipronil has an aerobic soil half-life of 188 d , which supports the finding that mean fipronil concentrations were similar over the 153 d period considered in this study. In addition, the gradual formation and increasing soil concentrations of fipronil degradates was consistent with the relatively slow degradation rate of the parent compound. Fipronil and fipronil sulfone were detected with the greatest frequency and at the highest maximum concentrations. Fipronil desulfinyl and fipronil sulfide were detected less frequently and at substantially lower maximum concentrations. Fiproles were measured in soil samples at detection frequencies similar to those measured in dust , but maximum soil concentrations were much lower than maximum dust concentrations. It is possible that soil concentrations were low relative to dust concentrations because soil samples were collected to a depth while dust particles partially originated from wind erosion of the surficial soil. Fiproles have been shown to be enriched in fine particles characteristic of urban dust ,ebb and flow trays suggesting that residues initially present in the surrounding soil may have contributed to contamination of loose dust particles on impervious surfaces.

Results summarized herein reveal that soil treated with fipronil-based pesticide formulations remains contaminated by fiproles for a significant amount of time following treatment and is a source of fipronil degradation products. These data collectively imply that soil has the potential to contribute fipronil and its degradation products to their loads in urban runoff. However, this contribution likely depends upon the entrance of soil particles into runoff, either by inundation of soil with a large runoff volume after a prolonged rainfall, an irrigation event, or by prior transport of soil particles onto urban impervious surfaces. Mean concrete concentrations of fiproles were at their highest 1 d after application and decreased subsequently by 57-89% at the 30 d sampling point. Fipronil was rapidly transformed after application such that its degradation products were detected at high mean concentrations 1 d after application. This finding was consistent with results of a recent study focused on the degradation of pesticides on urban hard surfaces, where it was observed that fipronil was rapidly transformed to its biologically active degradation products on concrete in bench and field experiments. Mean concentrations then remained relatively stable for the duration of the sampling campaign, with 30 d concentrations being similar to those at 79 d, 110 d, and 153 d. Detection frequencies of fiproles in concrete ranged from 27 to 92%, with maximum concentrations of 3.19-25.4 µg m-2.The most prevalent degradation product was fipronil sulfone , while fipronil desulfinyl was detected at a higher maximum concentration than the other degradates, second only to the parent compound. An investigation of the contribution of fine particles to the runoff loads of pyrethroid pesticides also revealed high concentrations of bifenthrin and permethrin on concrete following application of professional pesticide formulations. Concrete data further showed that fiproles were present in the concrete at detectable concentrations for several months after initial application of fipronil for pest treatment. This suggests that concrete may act as a long-term source of these compounds in urban runoff.

Several linear regression analyses were performed to assess the presence of statistically significant linear relationships between fiprole concentrations in different urban solid matrices and concentrations in runoff water.A statistically significant relationship would indicate that a given component may be an important source for fiproles in runoff. It was observed that statistically significant relationships existed between the runoff and concrete concentrations of fipronil desulfinyl, fipronil sulfide, fipronil, and fipronil sulfone. A previous study similarly uncovered a highly significant linear relationship between runoff concentrations of pyrethroids and their concentrations on concrete surfaces measured using a surface wipe method. In this study, significant relationships were also found between the runoff and dust concentrations of fipronil desulfinyl and fipronil. Recent studies have also implicated dust particles in the offsite transport of hydrophobic organic contaminants, but the present study was the first to directly evaluate the connection between dust and runoff loads of fiproles. The significance of the concrete-runoff and dust-runoff relationships for fiproles together suggested that dust on impervious urban surfaces and residues on concrete are important sources of fiproles in runoff. Statistical analysis, however, did not show soil as a significant source for fiproles in runoff water. As discussed above, even though soil was not a direct source, it is possible that soil particles in the surface layer may be transported via wind and other mechanisms onto impervious surfaces, indirectly contributing to the contamination of runoff water by fiproles. Soil particles likely represent a major component of urban dust; other components may include concrete fragments generated from weathering and plant debris. Taken together, the most important finding of this analysis was that the effectiveness of mitigation efforts would be improved by focusing on reduction of dust particles on impervious surfaces and prevention of pesticide contact with concrete surfaces such as driveways. Moreover, the established regression equations may be used to predict fiprole loads in runoff using levels in urban dust and residues on impervious surfaces, before a runoff event occurs.

Contamination of surface water by fiproles poses a threat to many benthic invertebrate species. Fiproles may therefore exert a significant effect on the benthic community structures of urban streams.However, even though runoff from a given residential area enters downstream surface water as a point source,4×8 flood tray surface runoff from individual homes in a neighborhood resemble nonpoint sources and is technically challenging to control. Identification of concrete surfaces and urban dust as the major sources of fiprole contamination of surface runoff at the site of pesticide treatment highlights their importance in the effort to reduce fiprole residues around a homesite, especially on impervious surfaces. The combination of rampant urbanization, rapid population growth, and global climate change has resulted in an extraordinary reduction in the potable and non-potable water supply worldwide. The deficiency of clean water supplies has led several nations, including the United States, to encourage a reduction in water use and pursue a myriad of water treatment and recycling initiatives. Water scarcity is exacerbated by pollution of surface water and ground water resources by anthropogenic contaminants such as pesticides. Indoor and outdoor use of insecticides in urban areas has been shown to cause contamination of urban surface water sources. Urban-use insecticides are incompletely removed at wastewater treatment plants before the release of effluent into surface streams, and runoff after rain and irrigation events further exacerbates surface water contamination. Fipronil and the synthetic pyrethroids are insecticides utilized at high rates in urban environments for professional and homeowner control of structural pest species such as ants, termites, spiders, and roaches, as well as for elimination of fleas and ticks in veterinary medications. Fipronil and its primary degradation products, fipronil desulfinyl, fipronil sulfide, and fipronil sulfone are moderately hydrophobic compounds while the pyrethroids are highly hydrophobic with log Kow =5.7-7.6. Numerous studies have shown occurrence of both insecticide classes in urban surface water at toxicologically relevant concentrations as well as in the sediment where residues may persist long after deposition. Furthermore, fipronil’s major degradation products exhibit toxicity equal to or greater than that of the parent compound. There is also evidence of additive pyrethroid toxicity in sensitive organisms. Fiproles and pyrethroids are easily transported in surface runoff and are present in WWTP effluents , aggravating the risk of toxicity to non-target aquatic species. In arid or semi-arid regions such as California, some urban streams are predominantly fed with urban runoff drainage and WWTP effluents.

Constructed wetlands are one potential solution to the shortcomings of WWTPs and the general lack of storm water treatment. They have been shown to remove nitrogen and phosphorous species, metals, antibiotic resistance genes, and various organic compounds. Existing data suggest that CWs are effective in reducing concentrations of fiproles and pyrethroids. However, field data on the performance of urban wetlands are limited, and in-depth information on the role of various wetland compartments is scarce. In this study, samples were collected from the Prado Wetlands, a 182 ha constructed treatment wetland system located in Southern California containing open water and vegetated cells, from June 2018-January 2019 and analyzed for fiproles and pyrethroids. The primary objectives were to determine the removal of these trace contaminants by the surface flow wetland, to understand the underlying processes most responsible for contaminant removal, and to estimate potential alleviations in invertebrate toxicity. It was hypothesized that sediment sorption and biodegradation would play a major role in the removal of fiproles and pyrethroids, resulting in reduced aquatic toxicity. Results from this study may be used to optimize the design of CWs and related water treatment systems to improve the quality of recycled water and to attenuate ecotoxicological and human health risks from potable and non-potable applications.Fipronil , fipronil desulfinyl , fipronil sulfide , and fipronil sulfone were obtained from the United States Environmental Protection Agency’s National Pesticide Standard Repository. Bifenthrin and deuterated bifenthrin were purchased from Toronto Research Chemicals. Cyfluthrin was purchased from Santa Cruz Biotechnology. Ethiprole was obtained from the Shanghai Pesticide Research Institute. Decachlorobiphenyl was purchased from AccuStandard.Solvents and other chemicals used were of pesticide or GC-MS grade. This study was undertaken at the Prado Wetlands in Corona, CA. This 182 ha complex of 45 surface flow wetland ponds was constructed in the 1990s and was initially established to remove NO3 – from the Santa Ana River. Up to 50% of the Santa Ana River flow, which consists primarily of treated wastewater during non-storm seasons, is diverted into the wetland system for treatment. Additional details regarding the Prado Wetlands are provided in the Supporting Information. The ponds selected for use in this study were cells S5 and S6 , which together constitute a 4.45 ha vegetated CW complete with inlet and outlet weir boxes. In the context of this study, this vegetated CW will be referred to as the Prado Constructed Wetland. The hydraulic retention time of the PCW was estimated to be 1.29 d based on the results of a pilot-scale rhodamine WT tracer experiment conducted at the Prado Wetlands. Samples and measurements were taken at the inlet weir box , the interface between ponds S5 and S6 following the connection pipe , and the outlet weir box. Water, sediment, and plant samples were collected from the PCW monthly during the period of June 2018-January 2019, with the exception of September 2018 when there were ongoing maintenance activities. Triplicate 1 L water samples were collected in amber glass bottles at the inlet, midpoint, and outlet of the PCW. Inlet and outlet samples were collected from the water flowing into the corresponding weir boxes, while midpoint samples were collected by placing bottles below the surface of the water against the direction of flow. Sample bottles were transported to the laboratory on ice and stored at 4 °C until extraction. Before extraction, water samples were passed through 0.7 µm filters to separate the TSS from the water. Filtered TSS samples were then dried in preparation for extraction. Wetland water samples were extracted using a method in Gan et al. , with modifications. Briefly, 30 mL of NaCl was combined with each water sample and liquid liquid extraction was performed with 60 mL aliquots of dichloromethane. Each extract was drained through a funnel containing anhydrous Na2SO4 to remove residual water, evaporated with a Büchi RE121 Rotovapor , and solvent exchanged into 9:1 hexane:acetone. Samples were then evaporated to approximately 0.5 mL under a gentle nitrogen stream and reconstituted in 1.0 mL hexane for analysis.