@article{jafarikouhini_sinclair_2024, title={Recovery of root hydraulic conductance and xylem vessel diameter following prolonged water deficit of maize}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.21161}, abstractNote={AbstractTo sustain crop growth following soil water deficit, it is essential to have rapid recovery of leaf gas exchange. One basis for rapid recovery would be the rapid return of root hydraulic conductance to predrought levels to support water transport to the plant shoot. In this study, transpiration and root hydraulic conductance were measured over a 9‐day recovery period following an initial water‐deficit treatment of three maize (Zea mays L.) cultivars. In addition, xylem vessel diameter was measured during the recovery period at different positions from the root tip. The initiation of recovery in the transpiration rate occurred in all three cultivars within 3 days after watering, although the root conductance and transpiration rate of one cultivar were much lower than the other two cultivars. Root conductance and vessel diameter increased more slowly than the recovery of transpiration. There was an indication that transpiration could have been limited by root hydraulic conductance only when its values were low during recovery. The relationship between hydraulic conductance and vessel diameter did not, however, indicate a Poiseuille's law relationship between the two variables. Overall, cultivar variability in recovery from water deficit of the transpiration rate and root hydraulic conductance indicates that the selection for rapid recovery of leaf gas exchange following water deficit could be an important component of genotype selection in maize breeding programs.}, journal={CROP SCIENCE}, author={Jafarikouhini, Nahid and Sinclair, Thomas R.}, year={2024}, month={Jan} }
 @article{sinclair_jafarikouhini_pradhan_2024, title={Unexpectedly, triple super phosphate fertilizer induces maize drought resilience}, ISSN={["1532-4087"]}, DOI={10.1080/01904167.2024.2325948}, abstractNote={Phosphorus fertilizer is commonly applied to soils in crop production as diammonium phosphate (DAP). To decrease ammonium addition to the environment, triple super phosphate (TSP) is being considered as a DAP replacement. This study was undertaken to compare the response of maize plants to soil fertilization with TSP vs. DAP under well-watered conditions, under soil-drying conditions, and root hydraulic conductance. It was found for well-watered conditions in a controlled environment that there was no difference in plant growth between DAP to TSP treatments. In soil dry-down experiments, however, the initiation of the decrease in transpiration rate was unexpectedly quite different between DAP and TSP treatments. The soil water content threshold for initiation of decrease in transpiration rate with DAP treatment (average fraction transpirable soil water for two experiments = 0.285) was consistent with common observations, but the threshold associated with TSP treatment occurred at an unusually high soil water content (average fraction transpirable soil water for two experiments = 0.545). The higher threshold with TSP resulted in an extended period of soil water use, i.e. soil water conservation. Soil water conservation resulting from the TSP treatment was associated with a 27% greater shoot mass accumulation following a 4-wk re-watering period after the water-deficit treatment than measured with the DAP treatment. The high threshold for decrease in transpiration resulting from TSP was consistent with measured lower root hydraulic conductance as compared to DAP treatment. The unexpected discovery of TSP-induced initiation of transpiration rate decrease at high soil water content is consistent with greater crop drought resilience.}, journal={JOURNAL OF PLANT NUTRITION}, author={Sinclair, Thomas R. and Jafarikouhini, Nahid and Pradhan, Deepti}, year={2024}, month={Feb} }
 @article{jafarikouhini_sinclair_2023, title={Hydraulic conductance and xylem vessel diameter of young maize roots subjected to sustained water-deficit}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.21023}, abstractNote={AbstractWater deficit can have large impacts on plants, including likely alteration of root hydraulic conductance and root xylem vessel diameter, which can decrease crop productivity. No results, however, exist to assess possible linkages between these two variables as critical components contributing to plant water status. This linkage was investigated in three maize (Zea mays L.) cultivars. A stable water‐deficit treatment was established and maintained in pots by allowing soil drying to the point where transpiration rate was held constant at about 0.5 of well‐watered pots. Initially, the root hydraulic conductance of the water‐deficit plants was equivalent to that of well‐watered plants. Subsequently, however, hydraulic conductance decreased substantially. The results for xylem vessel diameter at 5 cm from the root tip exhibited a pattern similar to the decrease in root hydraulic conductance. A graph of root hydraulic conductance versus xylem vessel diameter at 5 cm showed a curvilinear response with lessening in the increase in hydraulic conductance with increasing xylem vessel diameter. The results indicate a possible link between root conductance and xylem diameter but the conductance is much less sensitive to vessel diameter than the fourth power of the radius predicted by Poiseuille's law. The association between conductance and xylem vessel diameter may reflect interaction of radial and axial water flux through the root system as indexed by vessel radius in the zone near the root tip.}, journal={CROP SCIENCE}, author={Jafarikouhini, Nahid and Sinclair, Thomas R.}, year={2023}, month={May} }
 @article{echarte_sinclair_jafarikouhini_2023, title={Maize leaf rolling and its response to drying soil and evaporative demand}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.21002}, abstractNote={AbstractLeaf rolling is an adaptive mechanism associated with water deficiencies; however, the physiological processes and environmental factors contributing to leaf rolling are not fully understood. The objective of this study was to examine (i) a possible relationship between the degree of leaf rolling and soil water content and (ii) the possible influence of vapor pressure deficit (VPD) on the degree of leaf rolling. Leaf rolling was measured on maize (Zea mays L.) plants grown in pots and subjected to various soil drying and atmospheric VPD treatments. The experimental results indicated that (i) high VPD by itself does not readily induce leaf rolling, and (ii) leaf rolling was observed in proportion to the extent of soil drying. The values of the fraction of transpirable soil water thresholds for the decline in normalized transpiration rate and for the initiation of plant leaf rolling were sensitive to environmental conditions (VPD and temperature). With soil drying, leaf rolling was initiated slightly after the initiation of a decrease in the transpiration rate.}, journal={CROP SCIENCE}, author={Echarte, Laura and Sinclair, Thomas. R. R. and Jafarikouhini, Nahid}, year={2023}, month={May} }
 @article{jafarikouhini_sinclair_resende_2022, title={Comparison of water flow capacity in leaves among sweet corn genotypes as basis for plant transpiration rate sensitivity to vapor pressure deficit}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.20711}, abstractNote={AbstractGenotypes in crop species have been identified that initiate partial stomata closure at elevated atmospheric vapor pressure deficit (VPD), which results in conserved soil water for crop use during subsequent water‐deficit episodes and thereby allowing for possible yield increase. In sweet corn (Zea mays L), 17 genotypes have been previously identified with the VPD‐responsive trait, although the VPD value at the initiation of stomata closure varied among genotypes. A hypothesis to explain variation in transpiration response to VPD is that water flow capacity in the leaves differs among genotypes. To gauge water flow capacity in leaves, the rate of stomata opening was observed visually after stomata closure was induced by 3 kPa VPD. The stomata opening time was rapid and varied among genotypes from 90 to 179 s. However, there was no correlation between opening time and the VPD at which partial stomata closure was initiated in intact plants. An additional set of experiments was done to examine whether genotypic differences in a subpopulation of silver‐inhibited aquaporins might contribute to differences in leaf water flow. There was a correlation among genotypes between slow opening time of the stomata and greater inhibition of transpiration rate following feeding leaves with silver ion. However, the response to the silver treatment did not correlate with the VPD at which transpiration decrease of intact plants was initiated. These results indicate that the differences observed in the water flow capacity in sweet corn leaves were not major factors accounting for the genotypic differences in whole‐plant transpiration response to elevated VPD.}, journal={CROP SCIENCE}, author={Jafarikouhini, Nahid and Sinclair, Thomas R. and Resende, Marcio F., Jr.}, year={2022}, month={Feb} }
 @article{sinclair_jafarikouhini_2021, title={Interactive effects of level of nitrogen and irrigation application on maize yield}, ISSN={["1532-4087"]}, DOI={10.1080/01904167.2021.2020835}, abstractNote={Abstract Maize (Zea mays L.) yields are recognized to be sensitive to both the level of nitrogen fertilization and irrigation that is applied to the crop. However, there are virtually no studies where experimental results are analyzed to quantitatively explore directly the interactive influence of these two resources on yield. As a consequence, it is difficult to sort out the optimum management regime for the available resources. A polynomial regression analysis was applied to results from seven field experiments involving several nitrogen and irrigation treatments. The polynomial equation included for each resource a linear term and second-order term plus a multiplicative term of the two resources. The polynomial regression fit very well the results of all experiments (R2 ≥ 0.86). The impact of irrigation included the linear term in all experiments (p ≤ 0.017). In all but one experiment, yield was also linearly dependent on amount of nitrogen application. The polynomial expression led to determination of the nitrogen fertilization required for maximum yield as being dependent on level of irrigation. In all cases, increased irrigation amounts resulted in an increased nitrogen requirement to achieve maximum yield. Another important outcome of the analysis was that the multiplicative term for irrigation x nitrogen was generally important in describing yield. These results demonstrate the inadequacy of attempting to define the results of such multiple-factor experiments based on a single limiting-factor approach.}, journal={JOURNAL OF PLANT NUTRITION}, author={Sinclair, Thomas R. and Jafarikouhini, Nahid}, year={2021}, month={Dec} }
 @article{sinclair_jafarikouhini_2022, title={Plant waterflow restrictions among sweet corn lines related to limited-transpiration trait}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.20717}, abstractNote={AbstractWhile partial stomata closure under elevated vapor pressure deficit (VPD), that is, a limited‐transpiration trait resulting in soil water conservation and crop drought resiliency, has been identified in a few lines in all major crop species, the basis for the trait is not resolved. Since changes in stomatal aperture are associated with hydraulic processes, properties influencing waterflow in the plant are candidates associated with expression of limited‐transpiration. In a previous study with leaves of sweet corn (Zea mays L.), limited‐transpiration was only weakly associated with the effect of silver ion, an aquaporin inhibitor, on leaf transpiration rate. The hypothesis was explored that total aquaporin activity rather than only silver‐sensitive aquaporins may be more relevant in the expression of limited transpiration. Leaves were fed potent aquaporin inhibitors of mercury and peroxide which both resulted in greater transpiration inhibition than silver, but there were no differences in response among lines. A second hypothesis was that there may be a major limitation of waterflow in the root system accounting for genotypic variation in expression of the limited‐transpiration trait. No differences in root hydraulic conductance were found among sweet corn lines differing in the limited‐transpiration trait. However, it was discovered that the root conductance decreased during the photoperiod in all tested lines. Measurements of root hydraulic conductance in response to a silver treatment showed differences among lines with an association between the VPD breakpoint for limited transpiration and transpiration sensitivity to the silver treatment.}, journal={CROP SCIENCE}, author={Sinclair, Thomas R. and Jafarikouhini, Nahid}, year={2022}, month={Apr} }
 @article{chiango_jafarikouhini_pradhan_figueiredo_silva_sinclair_holland_2021, title={Drought resilience in CIMMYT maize lines adapted to Africa resulting from transpiration sensitivity to vapor pressure deficit and soil drying}, volume={8}, ISSN={["1542-7536"]}, DOI={10.1080/15427528.2021.1961334}, abstractNote={ABSTRACT Low rainfall limits crop yield, particularly for maize (Zea mays L.) in southern Africa. Consequently, there is a need to identify genetic sources of specific drought-related traits that can contribute to soil water conservation and increased yields under water-limited conditions. In this study, maize genotypes released for production in southern Africa were tested for expression of two soil water-conservation traits: limited transpiration under elevated vapor pressure deficit (VPD) and decreased transpiration rate at high soil water contents earlier in the soil drying cycle. Two genotypes, CML 590 and CML 593, were identified and confirmed to initiate expression of limited-transpiration rate at VPD above about 1.9 kPa. In the soil-drying experiment, Umbelu 8923 and Umbelu 8930 closed their stomata earliest in the soil drying cycle as compared to other tested genotypes. These four genotypes with specific physiological traits for superior response to water deficit are genetic resources for further study to improve maize drought resilience.}, journal={JOURNAL OF CROP IMPROVEMENT}, author={Chiango, H. and Jafarikouhini, N. and Pradhan, D. and Figueiredo, A. and Silva, J. and Sinclair, T. R. and Holland, J.}, year={2021}, month={Aug} }
 @article{jafarikouhini_kazemeini_sinclair_2021, title={Fresh sweet corn yield sensitivity to deficit nitrogen and water conditions}, ISSN={["1542-7536"]}, DOI={10.1080/15427528.2021.1995560}, abstractNote={ABSTRACT Water and nitrogen (N) are the major limitations for maximizing crop yield. However, there has been no detailed examination of these limitations on fresh kernel yield in sweet corn (Zea mays L.). A two-year field study in Shiraz, Iran, was conducted to document sweet corn response to three soil-water regimes (irrigation to field capacity, and 80% and 60% of this amount) and five N fertilizer amounts (0, 75, 125, 175, and 225 kg N ha−1). Decreasing irrigation to 60% of field capacity resulted in yield decreases. The results showed that increasing N amounts increased fresh kernel yield to a maximum at 175 and 225 kg N ha−1. A highly positive, linear correlation was found between fresh kernel yield and kernel number formed per ear (R2 = 0.94), and also between kernel fresh yield and total crop mass (R2 = 0.88). Harvest index (HI) based on dry kernel weight varied between 0.20 and 0.41 in the two years with the lowest HI occurring in the 0 and 75 kg N ha−1 treatments.}, journal={JOURNAL OF CROP IMPROVEMENT}, author={Jafarikouhini, Nahid and Kazemeini, Seyed Abdolreza and Sinclair, Thomas R.}, year={2021}, month={Oct} }
 @article{jafarikouhini_sinclair_resende_2021, title={Limited-transpiration rate and plant conductance in a diverse sweet corn population}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.20664}, abstractNote={AbstractLimited‐transpiration rate at elevated vapor pressure deficit (VPD) can allow soil water conservation for use during late‐season drought, but it can also result in decreased crop yields under well‐watered conditions because of restricted crop gas exchange. Previous studies with sweet corn (Zea mays L.) have found the limited‐transpiration rate was quite common among commercial cultivars even though sweet corn is commonly grown under well‐watered conditions. This study was undertaken to identify possible genetic sources of sweet corn that were not encumbered by the limited‐transpiration trait. Additionally, data were obtained to compare the plant hydraulic conductance among the lines. Among the 26 sweet corn lines included in this study, only eight did not express the limited‐transpiration trait. Four of the lines not expressing the limited‐transpiration (IL395a, IL543c, P39, and SD245) had stomata vapor conductance values over the range of tested VPD similar to the values expressed by many of the limited‐transpiration lines only at low VPD. The eight lines not expressing the limited‐transpiration trait tended to have low plant hydraulic conductance. For those lines expressing the limited‐transpiration trait, there was a correlation between the VPD at initiation of limited transpiration and plant hydraulic conductance. Expression of the limited‐transpiration traits proved, however, to be temperature sensitive in 7 of 18 tested lines expressing the trait at 32 °C because they failed to express the trait at 38 °C. The genetic variation in expression of the limited‐transpiration trait and plant hydraulic conductance identified in this study offers specific candidate inbred lines that could be used as genetic resources for improving sweet corn growth and yield for well‐watered environments.}, journal={CROP SCIENCE}, author={Jafarikouhini, Nahid and Sinclair, Thomas R. and Resende, Marcio F. R.}, year={2021}, month={Dec} }
 @article{jafarikouhini_pradhan_sinclair_2020, title={Basis of limited-transpiration rate under elevated vapor pressure deficit and high temperature among sweet corn cultivars}, volume={179}, ISBN={1873-7307}, DOI={10.1016/j.envexpbot.2020.104205}, abstractNote={One plant trait that has been developed in several crop species to increase the effectiveness in water use through the cropping season is limited-transpiration under elevated atmospheric vapor pressure deficit (VPD). This trait allows water conservation early in the season so that there is more soil water available late in the season for sustained physiological activity during seed development. In sweet corn (Zea mays L. saccharata), where the quality of the kernels is important, this trait could prove to be especially beneficial. The background objective of this study was to explore 16 sweet corn cultivars for expression of the limited-transpiration trait. It was found at 32 °C that 13 of the 16 cultivars expressed the trait. It was found in a subset of eight of these cultivars, however, only half retained the limited-transpiration trait at 38 °C. The additional objectives were to explore the hypotheses that expression of the limited-transpiration trait was related to plant hydraulic conductance, and to the abundance of silver-sensitive aquaporins in the leaves. In cultivars that lost expression of the limited-transpiration trait at 38 °C there were large increases in plant hydraulic conductance at 38 °C as compared to 32 °C. Abundance of silver-sensitive aquaporins was related to the transpiration rate under low VPD conditions. That is, those cultivars with more abundant silver-sensitive aquaporins had greater transpiration rates as a result of greater stomatal conductance. These results showed that while expression of the limited-transpiration trait in sweet corn at 32 °C was common, differences in expression of the trait at 38 °C were observed due to differences in plant hydraulic conductance and stomatal conductance.}, journal={ENVIRONMENTAL AND EXPERIMENTAL BOTANY}, author={Jafarikouhini, Nahid and Pradhan, Deepti and Sinclair, Thomas R.}, year={2020}, month={Nov} }
 @article{jafarikouhini_kazemeini_sinclair_2020, title={Sweet corn nitrogen accumulation, leaf photosynthesis rate, and radiation use efficiency under variable nitrogen fertility and irrigation}, volume={257}, ISSN={["1872-6852"]}, DOI={10.1016/j.fcr.2020.107913}, abstractNote={Virtually no information exists on the response of sweet corn (Zea mays L. saccharata) to nitrogen fertility and irrigation treatments in terms of leaf nitrogen accumulation and the consequent impact on leaf CO2 assimilation rate and on crop growth as measured as radiation use efficiency (RUE). A two-year field experiment was undertaken in which a sweet corn cultivar was subjected to all combinations of five nitrogen fertility and three irrigation treatments. Leaf photosynthesis measurements were made at stages of 7–9 leaves, tasseling, silking, blistering, and milking. Leaf nitrogen per unit area was also measured at these five stages plus two additional stages before and after the five core measurements. Total nitrogen and plant mass was accumulated at the seven stages to track total nitrogen accumulation and to calculate RUE. The overall patterns in the measured variables were similar to those reported for field maize. However, leaf nitrogen per unit area for sweet corn under optimum conditions was greater than reported for field maize. The higher leaf nitrogen per unit area in sweet corn did not, however, result in greater leaf photosynthesis rates and RUE than reported for field maize. The results of these unique observations on sweet corn indicate the possibility of greater nitrogen storage in sweet corn leaves that is not directly linked with photosynthesis and carbon accumulation.}, journal={FIELD CROPS RESEARCH}, author={Jafarikouhini, Nahid and Kazemeini, Seyed Abdolreza and Sinclair, Thomas R.}, year={2020}, month={Oct} }