Indiana University-Purdue University Indianapolis (IUPUI) / Invasive exotic species have caused severe ecological and economic damages to many communities in the United States and elsewhere. It is therefore important to improve our understanding of how global environmental changes will affect the invasiveness and severity of these invasive species. Over the last century, anthropogenic activities have caused multiple environmental changes. Previous studies have generally focused on the impact of the increasing atmospheric CO2 level on the physiology and growth of invasive species. With atmospheric nitrogen (N) deposition on the rise over the past decades, it is essential to recognize how an increase in soil N will affect the invasiveness of some exotic species. To determine the impact of increased atmospheric N deposition and drought stress on invasive species, I studied the impact of different levels of N on Alliaria petiolata (garlic mustard), an exotic invasive species. In addition, I examined the interactive effects of N deposition and drought stress on garlic mustard. Multiple morphological measurements were used to analyze the growth rate at varying levels of N and soil moisture. The study on N deposition on plant growth will improve our understanding of the invasiveness of garlic mustard. The changes in precipitation patterns must also be examined to foresee if plants in increased atmospheric N conditions can overcome drought stress conditions. I found an increase in plant growth and photosynthetic rate at higher levels of N. Plants with adequate water displayed a continued increase from the lowest level to the highest level of N. Increases in drought stressed plants plateaued at an intermediate N level of 20 kg ha-1. My results demonstrated that during drought stress garlic mustard does not benefit from an increase in N above a certain level. These results are important to take into consideration when we analyze the spreading of invasive weeds due to global environmental changes, including increased atmospheric N deposition and regional drought, in order to apply the optimal management strategies for controlling invasive species.

Drought is a natural disaster, which negatively affects millions of people and causes huge economic losses. This thesis investigates agricultural drought in Czechia using machine learning algorithms. The statistical models utilised were Random Forest (RF), Geographical Random Forest (GRF) and Locally Tuned Geographical Random Forest (LT GRF). GRF consists of several RF models trained on a subset of original data. The final prediction is a weighted sum of the prediction of a local and global model. The size of the subset is determined by the tunable parameter. LT GRF addresses spatial variability of subset size and local weight. During the tuning process, optimal parameters are found for every location and then interpolated for unknown regions. The thesis aims to evaluate the performance of each model and compare GRF feature importance output with the global model. The best model features meteorological impor- tances are used to create a drought vulnerability map of Czechia. Produced assessment is compared to existing drought vulnerability projects. 1

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第17964号 / 農博第2032号 / 新制||農||1019(附属図書館) / 学位論文||H25||N4808(農学部図書室) / 30794 / 京都大学大学院農学研究科農学専攻 / (主査)教授 白岩 立彦, 教授 奥本 裕, 教授 稲村 達也 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Drought and temperature stress are the two most important factors limiting crop productivity. A physiological and proteomic analysis of soybean was performed to investigate the negative impact of these variables. The previous studies reported the beneficial effect of silicon under stress conditions. Silicon supplementation may promote plant growth under drought stress, although the mechanism to alleviate drought stress is uncertain. The proteomic analysis of chloroplast proteins was carried out to study the response of silicon supplementation under drought stress. Similarly, temperature stress, mainly heat stress, has an adverse effect on soybean plants. The comparative analysis of two soybean cultivars, DS25-1 and DS31-243 was examined under ambient and elevated CO2 levels. The proteomic study employed two-dimensional gel analysis and mass spectrometry techniques to identify differentially expressed proteins under drought and temperature stress. The identified proteins are involved in metabolic processes, photosynthesis, signaling, redox homeostasis, and other cellular pathways. Most of these proteins were involved in metabolism, response to heat and photosynthesis showing significant cross-tolerance mechanisms. The physiological parameters like stomatal conductance, transpiration, photosynthesis, and chlorophyll pigments were also studied. Silicon application improved plant growth under drought stress. However, at the elevated CO2 level, plants showed better growth under heat stress. Together, these findings suggested the role of silicon and elevated CO2 concentration in drought and temperature stress in soybean. The differentially expressed proteins helped mitigate the negative impact of these stress, mainly the photosynthetic, antioxidant and heat shock proteins, and enhance crop growth and productivity under drought and heat stress.

The chromosome substitution (CS) lines constitute an important genetic and breeding resources, increasing the genetic diversity of Upland cotton from other alien tetraploid species. Two experiments were conducted to quantify low temperature and drought stress effects during early growth stages in 21 cotton CS-lines with parent, Texas Marker (TM)-1. In Experiment I, plants were grown at optimum (30/22°C) and low (22/14°C) temperatures under optimum water and nutrient conditions. In Experiment II, plants were grown at optimum water and drought conditions. Above- and below-ground growth parameters including several root traits were assessed at 25 days after seeding. CS-lines varied significantly varied for many traits measured. Combined low temperature and drought response indices, derived from all measured parameters, showed CS-T04 and CSB08sh showed significantly higher and lower tolerance to low temperature, respectively, while CS-T04 and CS-B22sh showed significantly higher and lower tolerance to drought condition compared to TM-1.

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Droughts are a common disturbance experienced by forest systems across the southeastern United States and are expected to increase in frequency in the near future. Few empirical studies have evaluated the response of individual tree resistance and resilience following silvicultural treatment in longleaf pine (Pinus palustris Mill.). This study evaluates the differences in drought responses between two forests during three different periods. The first period evaluated pretreatment (2000) conditions, while the second (2006), and third (2011) compared conditions after the implementation of five silvicultural treatments. The main findings are that, as additional basal area is removed, both individual tree resistance and resilience to drought increase. Moreover, as drought intensity decreases, both resistance and resilience metrics increase. Finally, higher competitive status of individual trees warranted higher resistance to drought compared to trees of a lower competitive status.

California state officials have continued to warn and encourage preparedness for the growing threats of water scarcity. This puts pressure on water suppliers to develop technological and managerial solutions to alleviate the problems associated with scarcity. A recent popular management strategy for distributing water is encouraging water transfers. While there has been analyses on water transfers between large districts and agencies, little analysis has been completed for smaller scale trades, i.e. between individuals in the same water district. This analysis models an agricultural water district, based on the Berrenda Mesa Water District (BMWD). In the model, the growers in the district have the collective goal of profit maximization, and the district has the goal of maximizing revenue from agriculture. The district decides if either long term or short term transfers are allowed between growers, who themselves decide to either elect to save more water or trade more water. A game theory simulation model is used to determine the best cooperative management strategy (BCSC), which is defined as a strategy combination which is Pareto optimal and a Nash equilibrium, or Pareto optimal and there are no Nash equilibria. Ultimately, the strategy combination of the district allowing short term trades and the growers electing to sell more water is the BCSC in all tested water scarcity scenarios.

The drought response of the extremophile Eutrema salsugineum (Thellungiella salsuginea) was studied using an experimental protocol involving two progressive drought exposures separated by a recovery period. Accessions from the Yukon Territory, Canada, and Shandong Province, China, were distinguished with respect to their responses to the initial drought, their recovery from wilting, and their response to a subsequent drought following recovery. Eutrema cauline leaves and rosettes were sampled at different stages of the drought treatment for water status and biomass measurements and this information guided tissue selection for transcriptome sequencing by RNA-Seq. For Yukon plants, the initial drought led to a 46% reduction in stomatal conductance (from 122.3 to 66.3 mol m-2s-1) and 25% reduction in rosette water loss relative to unstressed control plants, evidence of drought avoidance to conserve water. Yukon leaf solute potentials decreased to -1.83 MPa compared to -1.54 MPa for Shandong leaves indicating that more solutes accumulated in Yukon leaves in response to drought. Upon wilting, Yukon plants re-established turgor at significantly lower leaf solute potentials than the level for well-watered Yukon plants consistent with osmotic adjustment. In contrast, leaf solute potentials in re-watered Shandong plants returned to pre-drought levels (-1.6 MPa). During the second drought exposure, leaf water content and specific leaf area measurements were significantly higher in Yukon plants compared to plants experiencing the initial drought and wilting was delayed relative to Shandong plants. At the transcriptional level, the initial drought exposure resulted in over 2000 differentially expressed genes in leaves of Yukon plants compared to only two in Shandong plants. Following exposure to a second drought only 45 genes were differentially expressed in leaves of Yukon plants while Shandong plants underwent substantial transcriptional re-programming with nearly 500 genes showing differential expression. Studies of Eutrema grown under controlled conditions were supplemented by physiological measurements made using Eutrema plants found on saline soils in the Yukon. The average stomatal conductance for field plants was 84.8 mol m-2s-1, a rate similar to that of drought-treated Yukon plants in the cabinet. Leaf solute potentials of field plants ranged from -2.0 MPa to -3.5 MPa. RT-qPCR showed the relative expression of four dehydrin-encoding genes, EsRAB18, EsRD22, EsRD29A, and EsERD1, was high in the field plants and levels of expression were comparable to drought-stressed cabinet plants. In summary, Eutrema salsugineum has a naturally high tolerance to water deficits. Between the two accessions studied, Yukon plants have a superior capacity to withstand drought relative to Shandong plants. The heightened capacity for Yukon plants to recover from drought and tolerate repeated drought exposures makes this accession a particularly valuable model for studying many mechanisms underlying innate and inducible plant tolerance to drought. / Thesis / Doctor of Philosophy (PhD)

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