Tag: growing blueberries

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Growing Up Without Ground: The Basics of Hydroponic Crop Cultivation

There may be some regulation controlled by a threshold value for Cd plant status, in both species. Long-term contamination with 0.1 µM would be below this threshold, thanks to the PC sequestration for example. On the other hand, long-term contamination with 10 µM would exceed this limit and result in down-regulation of the transport proteins of the HATS, possibly because of excess free Cd in the cytosol or because of some signal from the shoots. For both plants, cell wall sorption efficiency appears to be improved by the high Cd concentration in the growth solution, whereas the low concentration had generally no significant impact. The increase in the cell wall binding efficiency after high internal Cd accumulation may be related to the down-regulation of intracellular uptake. However, the reduction in symplastic influx is very low and cannot account for the increase observed at the apoplastic level. On the contrary, the up-regulation of the adsorption rate may well account for the decrease in the symplastic uptake. The apparent up-regulation of Cd binding properties may be due to modifications of the root cell-wall adsorption characteristics, particularly the root CEC. Cadmium stress is known to affect cell wall composition. First, Cd increases the proportion of acidic pectins . Secondly, the cell wall CEC may be increased through regulation of enzymes. For instance, pectinmethylesterase has been suggested to be stimulated in the outer cell wall domains of Cd-stressed plants, resulting in a strong decrease in the methylesterification of the acidic pectins. Thus, Cd strongly increases the acid pectins/esterified pectins ratio, hence the higher CEC, particularly in the middle lamellae . This low degree of esterification enhances the adsorption of all metallic trace elements , improving the plant tolerance of the metal. As dry mass did not vary with the level of contamination,40 litre pot there may be no significant difference in the proportion of young roots and then no decrease in the root CEC due to the age of roots.

Therefore, the insignificant effect of low Cd contamination on the apoplastic adsorption rate could be accounted for by the existence of some Cd-stress threshold below which there is no regulation mechanism. A long-lasting tolerance to aluminum ion is an essential phenotype for perennial plants growing on strong acid soils for longer periods. There is increasing evidence that plants with superior Al tolerances are relatively easily found in woody plants, such as tropical plantation trees Melaleuca cajuputi and Paraserianthes falcataria . Some woody plants, including tea, hydrangea, and Melastoma malabathricum, are also known as Al-accumulators that retain large amounts of Al in their above ground organs . However, the mechanisms responsible for high Al tolerance or high Al accumulation in woody plants remain to be elucidated. Our preliminary screening has successfully identified that root elongation in seedlings of Cinnamomum camphora, an evergreen tree widely distributed or planted in China and its neighboring regions, is much less inhibited even at high Al concentrations in a simple ionic solution at least for several days. Our finding is consistent with a study that reported no growth reduction in C. camphora seedlings against Al in a nutrient solution for 5 weeks . As a first step in understanding long-term Al tolerance mechanisms in seedlings of C. camphora, we employed a pulse Al exposure every two days for 60 days in measurements of root elongation and Al accumulation in each organ. To understand Al transport mechanisms in shoots, we also examined the Al accumulation patterns in branch cuttings of C. camphora. Root architecture influences nutrient and water uptake, anchorage, and mechanical support, interactions with microbes, and responses to various abiotic stress factors . Since water and mineral supply are often limited in the soil, a plant with a more extensive root system exhibits higher performance with regard to the tolerance of drought and poor nutrient conditions . Several factors, including root angle, root growth rate, and root types, influence root architecture . Root growth requires the successive formation of new cells from stem cells in the root apical meristem , and the progeny of such stem cells divide rapidly and enter the elongation/differentiation zone . To maintain root meristem activity, the rates of cell division and differentiation have to be coordinated .

Plant hormones greatly influence the balance between cell division and cell differentiation . In addition, the interaction between cytokinin and auxin determines the size of the RAM through the regulation of the genes involved in auxin signaling and/or transport to ensure an appropriate auxin gradient . The rice root system consists of one seminal root, numerous adventitious roots, and lateral roots that emerge from the other two types . Lateral roots are the major components involved in the absorption of nutrients and in interactions with the surrounding soil environment . Lateral root formation represents a complex developmental process modulated by several hormones, including auxin and ethylene . Well defined and closely coordinated cell division activities give rise to lateral root primordia . While lateral roots originate from pericycle cells adjacent to xylem poles in Arabidopsis , pericycle and endodermal cells located near phloem poles are the origins of lateral roots in rice and maize . Their development is initiated by the asymmetric division of the pericycle cells, and subsequent divisions result in the formation of dome-shaped, multilayered, lateral root primordia . After the initiation of asymmetric division, the primordia emerge, form active meristems, and break through the epidermal cells to become new lateral roots. Auxin is essential for various steps in the course of root development—from cell fate acquisition to meristem initiation, emergence, and elongation . In Arabidopsis, auxin is mainly synthesized in young apical tissues of the shoots and roots . Indole-3-acetic acid is considered the major form of auxin, with tryptophan being its precursor . Among the four pathways of IAA biosynthesis from Trp, the indole-3-pyruvic acid pathway is the major pathway in Arabidopsis . In the IPyA pathway, tryptophan aminotransferases convert Trp into IPyA, and YUCCAs synthesize IAA from IPyA, a rate-limiting step for the pathway .

In rice, FISH BONE encodes a Trp aminotransferase; loss of function results in pleiotropic abnormal phenotypes, which include small leaves with large lamina joint angles, unusual vascular development, and defects in root development, which are all consistent with a decrease in internal IAA levels . Mutations in CONSTUTIVELY WILTED1result in narrow and rolled leaves, in addition to the decreased growth of lateral and crown roots . Conversely, the over expression of OsYUC1 causes an increase in IAA accumulation, and auxin-overproducing phenotypes are observed . Such phenotypes are subject to the presence of the transcription factor WUSCHEL-RELATED HOMEOBOX 11 , a key regulator of root development . In rice, auxin induces WOX11 transcription,collection drainage which establishes the YUCCA–auxin–WOX11 module for root development . Ethylene also controls root development. Treatment with low concentrations of an ethylene precursor, 1-aminocyclopropane- 1-carboxylic acid , promotes the initiation of lateral root primordia. In contrast, exposure to higher ACC concentrations inhibits such initiation considerably, while also promoting the growth of already existing lateral root primordia . The regulation is linked tightly with auxin . For example, ethylene application results in the accumulation of auxin at the tip of Arabidopsis primary roots through the promotion of auxin synthesis mediated by WEAK ETHYLENE INSENSIVE2/ANTHRANILATE SYNTHASE α1 and WEI7/INSENSIVE2/ ANTHRANILATE SYNTHASE β1 . WEI2 and WEI7 encode the α and β subunits, respectively, of anthranilate synthase , a rate-limiting enzyme in the biosynthesis of the auxin precursor Trp . In rice, ethylene also increases endogenous IAA concentrations in the roots; however, the effect is minimized in mutants defective in YUC8/REIN7, which participates in auxin biosynthesis . The homeobox genes are critical for growth and development because they regulate cell fate and plant specificity . A family of zinc-finger homeodomain proteins has an N-terminal conserved domain containing several cysteine and histidine residues for potential zinc binding, in addition to a C-terminal domain containing a homeodomain . Most ZF-HD proteins do not have an intrinsic activation domain, which suggests that interactions with other factors are necessary for transcriptional activation . In addition, all 14 members of the ZF-HD gene family in Arabidopsis are predominantly expressed in floral tissues and play key roles in their development . One member, AtHB33, which is negatively regulated by ARF2, is required for seed germination and primary root growth . Among the 11 ZF-HD genes in rice, the over expression of OsZHD1 and OsZHD2 induces leaf curling by controlling the number and arrangement of bulliform cells . Here, we report that the over expression of OsZHD2 in rice improves root growth by enhancing meristem activity. We demonstrated that the homeobox protein elevated ethylene concentrations by increasing the transcript levels of ethylene biosynthesis genes. We further obtained ChIP assay data that revealed an interaction between OsZHD2 and the chromatin of ACS5. Analyses of transgenic rice plants carrying DR5::GUS and DR5::VENUS revealed that the expression of the DR5 reporter gene was induced following treatment with ACC, an ethylene precursor. The results suggest that OsZHD2 increases the biosynthesis of ethylene and subsequently auxin, which stimulates root growth.We isolated a rice mutant plant with an extensive root system from a population of activation tagging lines, in which the expression of a gene is enhanced by multiple copies of the 35S enhancer introduced using T-DNA .

In Line 3A-13017, the root biomass increased significantly . At 8 DAG the seminal roots were 27% longer in the activation plants than in the WT . Their lateral roots were also much longer than in the WT at a similar stage. At the upper parts of the seminal roots, the mutant lateral roots were 144% longer than those of the WT . This activation line also had more lateral roots—230 per seminal root for Line 3A-13017 versus 179 laterals per seminal root for the WT . However, the density of lateral roots did not differ significantly between the genotypes , which indicated that the increase in the number of lateral roots was largely due to the mutant plants having longer primary roots. We located T-DNA 5 kb downstream from the stop codon of OsZHD2 in the transgenic line . Its expression was significantly higher than that of the control, potentially because of the 35S enhancer elements in the T-DNA border region . We designated this activation line as OsZHD2-D.qRT-PCR analysis revealed that the expression level of OsZHD2 was significantly higher in the root tips when compared with levels in the total root . In addition, the expression level of OsZHD2 was significantly higher in the basal parts of shoots including the SAM compared with upper parts of the shoots that contain leaf blades and sheathes . RNA in situ hybridization experiments revealed that OsZHD2 transcripts were abundant in the root tip regions . Several homeobox genes have been identified as key regulators of cell proliferation and specification at the early stages of embryogenesis in plants. Among 107 homeobox genes identified in the rice genome, the expression profiles from 93 members in different tissues during various developmental stages have been analyzed . The results of the analyses revealed that OsZHD2 is highly expressed in the SAM . To evaluate whether OsZHD2 induces meristem activity, we treated seedling plants with 10 µM EdU, a thymidine analog, for 2 h to visualize the S-phase cells that actively incorporate EdU into DNA . The assay results revealed that OsZHD2-D had a higher number of S-phase cells in the RAM compared with the number of cells in the WT . The RAM region is defined based on the number of cells in a file that extend from the quiescent center to the first elongated cell . Quantifying such epidermis cells in the meristem region of lateral roots revealed that the number increased significantly in the activation line—25 versus 15 for the WT —which suggested that enhanced OsZHD2 expression led to the elongation of the RAM region.To confirm that the phenotypes observed from OsZHD2-D were due to the elevated expression levels of OsZHD2, we generated transgenic plants that expressed full-length OsZHD2 cDNA under the control of the maize Ubi promoter . From six independently transformed plants, we selected two lines, OX2 and OX4, which expressed OsZHD2 at high levels . Both had more extensive root systems compared with those of the out segregated WT . Their seminal roots and lateral roots were also significantly longer , and the plants had more lateral roots than the WT . However, the density of lateral roots did not vary among genotypes .

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The hedonic approach attempts to measure directly the effect of climate on land values

There is a growing consensus that emissions of greenhouse gases due to human activity will lead to higher temperatures and increased precipitation. It is thought that these changes in climate will impact economic well being. Since temperature and precipitation are direct inputs in agricultural production, many believe that the largest effects will be in this sector. Previous research on the benchmark doubling of atmospheric concentrations of greenhouse gases is inconclusive about the sign and magnitude of its effect on the value of US agricultural land . Most previous research employs either the production function or hedonic approach to estimate the effect of climate change.Due to its experimental design, the production function approach provides estimates of the effect of weather on the yields of specific crops that are purged of bias due to determinants of agricultural output that are beyond farmers’ control . Its disadvantage is that these experimental estimates do not account for the full range of compensatory responses to changes in weather made by profit maximizing farmers. For example in response to a change in climate, farmers may alter their use of fertilizers, change their mix of crops, or even decide to use their farmland for another activity . Since farmer adaptations are completely constrained in the production function approach, it is likely to produce estimates of climate change that are biased downwards. Its clear advantage is that if land markets are operating properly, prices will reflect the present discounted value of land rents into the infinite future. In principle, this approach accounts for the full range of farmer adaptations. The limitation is that the validity of this approach requires consistent estimation of the effect of climate on land values.

Since at least the classic Hoch and Mundlak papers,growing blueberries it has been recognized that unmeasured characteristics are an important determinant of output and land values in agricultural settings.2 Consequently, the hedonic approach may confound climate with other factors and the sign and magnitude of the resulting omitted variables bias is unknown. In light of the importance of the question, this paper proposes a new strategy to estimate the effects of climate change on the agricultural sector. We use a county-level panel data file constructed from the Censuses of Agriculture to estimate the effect of weather on agricultural profits, conditional on county and state by year fixed effects. Thus, the weather parameters are identified from the county specific deviations in weather about the county averages after adjustment for shocks common to all counties in a state. This variation is presumed to be orthogonal to unobserved determinants of agricultural profits, so it offers a possible solution to the omitted variables bias problems that appear to plague the hedonic approach. Its limitation is that farmers cannot implement the full range of adaptations in response to a single year’s weather realization, so its estimates of the impact of climate change are biased downwards. Our analysis begins with a reexamination of the evidence from the hedonic method. There are two important findings. First, the observable determinants of land prices are poorly balanced across quartiles of the long run temperature and precipitation averages. This means that functional form assumptions are important in this approach. Further, it may suggest that unobserved variables are likely to covary with climate. Second, we replicate the previous literature’s implementation of the hedonic approach and demonstrate that it produces estimates of the effect of climate change that are very sensitive to decisions about the appropriate control variables, sample and weighting.

We find that estimates of the effect of the benchmark doubling of greenhouse gasses on the value of agricultural land range from -$420 billion to $265 billion , which is an even wider range than has been noted in the previous literature. Despite its theoretical appeal, the wide variability of these estimates suggests that the hedonic method may be unreliable in this setting.The results from our preferred approach suggest that the benchmark change in climate would reduce annual agricultural profits by $2 to $4 billion, but the null effect of zero cannot be rejected. When this reduction in profits is assumed permanent and a discount rate of 5% is applied, the estimates suggest that the value of agricultural land is reduced by $40 to $80 billion, or –3% to –6%. Notably, we find modest evidence that farmers are able to undertake a limited set of adaptations in response to weather shocks. In the longer run, they can engage in a wider variety of adaptations, so our estimates are downwards biased relative to the preferred long run effect. Together the point estimates and sign of the likely bias contradict the popular view that climate change will have substantial negative effects on the US agricultural sector. In contrast to the hedonic approach, these estimates of the economic impact of global warming are robust. For example, the overall effect is virtually unchanged by adjustment for the rich set of available controls, which supports the assumption that weather fluctuations are orthogonal to other determinants of output. Further, the qualitative findings are similar whether we adjust for year fixed effects or state by year fixed effects . This finding suggests that the estimates are due to output differences, not price changes. Finally, we find substantial heterogeneity in the effect of climate change across the United States. The largest negative impacts tend to be concentrated in areas of the country where farming requires access to irrigation and fruits and vegetables are the predominant crops .

The analysis is conducted with the most detailed and comprehensive data available on agricultural production, soil quality, climate, and weather. The agricultural production data is derived from the 1978, 1982, 1987, 1992, and 1997 Censuses of Agriculture and the soil quality data comes from the National Resource Inventory data files from the same years. The climate and weather data are derived from the Parameter-elevation Regressions on Independent Slopes Model . This model generates estimates of precipitation and temperature at small geographic scales, based on observations from the more than 20,000 weather stations in the National Climatic Data Center’s Summary of the Month Cooperative Files during the 1970-1997 period. The PRISM data are used by NASA, the Weather Channel, and almost all other professional weather services. The paper proceeds as follows. Section I motivates our approach and discusses why it may be an appealing alternative to the hedonic and production function approaches. Section II describes the data sources and provides some summary statistics. Section III presents the econometric approach and Section IV describes the results. Section V assesses the magnitude of our estimates of the effect of climate change and discusses a number of important caveats to the analysis. Section VI concludes the paper. The production function approach relies on experimental evidence of the effect of temperature and precipitation on agricultural yields. The appealing feature of the experimental design is that it provides estimates of the effect of weather on the yields of specific crops that are purged of bias due to determinants of agricultural output that are beyond farmers’ control . Consequently, it is straightforward to use the results of these experiments to estimate the impacts of a given change in temperature or precipitation. Its disadvantage is that the experimental estimates are obtained in a laboratory setting and do not account for profit maximizing farmers’ compensatory responses to changes in climate. As an illustration, consider a permanent and unexpected decline in precipitation. In the short run,square plant pots farmers may respond by increasing the flow of irrigated water or altering fertilizer usage to mitigate the expected reduction in profits due to the decreased precipitation. In the medium run, farmers can choose to plant different crops that require less precipitation. And in the long run, farmers can convert their land into housing developments, golf courses, or some other purpose. Since even short run farmer adaptations are not allowed in the production function approach, it produces estimates of climate change that are downward biased. For this reason, it is sometimes referred to as the “dumb-farmer scenario.”

In an influential paper, Mendelsohn, Nordhaus, and Shaw proposed the hedonic approach as a solution to the production function’s shortcomings . The hedonic method aims to measure the effect of climate change by directly estimating the effect of temperature and precipitation on the value of agricultural land. Its appeal is that if land markets are operating properly, prices will reflect the present discounted value of land rents into the infinite future. To successfully implement the hedonic approach, it is necessary to obtain consistent estimates of the independent influence of climate on land values and this requires that all unobserved determinants of land values are orthogonal to climate.4 We demonstrate below that temperature and precipitation normals covary with soil characteristics, population density, per capita income, latitude, and elevation. This means that functional form assumptions are important in the hedonic approach and may imply that unobserved variables are likely to covary with climate. Further, recent research has found that cross sectional hedonic equations appear to be plagued by omitted variables bias in a variety of settings .5 Overall, it may be reasonable to assume that the cross-sectional hedonic approach confounds the effect of climate with other factors . This discussion highlights that for different reasons the production function and hedonic approaches are likely to produce biased estimates of the economic impact of climate change. It is impossible to know the magnitude of the biases associated with either approach and in the hedonic case even the sign is unknown. In this paper we propose an alternative strategy to estimate the effects of climate change. We use a county-level panel data file constructed from the Censuses of Agriculture to estimate the effect of weather on agricultural profits, conditional on county and state by year fixed effects. Thus, the weather parameters are identified from the county-specific deviations in weather about the county averages after adjustment for shocks common to all counties in a state. This variation is presumed to be orthogonal to unobserved determinants of agricultural profits, so it offers a possible solution to the omitted variables bias problems that appear to plague the hedonic approach. This approach differs from the hedonic one in a few key ways. First, under an additive separability assumption, its estimated parameters are purged of the influence of all unobserved time invariant factors. Second, it is not feasible to use land values as the dependent variable once the county fixed effects are included. This is because land values reflect long run averages of weather, not annual deviations from these averages, and there is no time variation in such variables. Third, although the dependent variable is not land values, our approach can be used to approximate the effect of climate change on agricultural land values. Specifically, we use the estimates of the effect of weather on profits and the benchmark estimates of a uniform 5 degree Fahrenheit increase in temperature and 8% increase in precipitation to calculate the expected change in annual profits . Since the value of land is equal to the present discounted stream of rental rates, it is straightforward to calculate the change in land values when we assume the predicted change in profits is permanent and make an assumption about the discount rate. Since climate change is a permanent phenomenon, we would like to isolate the long run change in profits. Consider the difference between the first term in equation in the short and long run in the context of a change in weather that reduces output. In the short run, supply is likely to be inelastic , which means that Short Run > 0. This increase in prices will help to mitigate farmers’ losses due to the lower production. However, the supply of agricultural goods is more elastic in the long run, so it is sensible to assume that Long Run is smaller in magnitude and perhaps even equal to zero. Consequently, the first term may be positive in the short run but small, or zero in the long run. Although our empirical approach relies on short run variation in weather, it may be feasible to abstract from the change in profits due to price changes . Recall, the price level is a function of the total quantity produced in the relevant market in a given year.