Collaborative Research: High Nighttime Stomatal Conductance and Transpiration in Plants

水是全球植物生产力的关键限制因素。 尽管植物中已经进化出许多减少水分流失的机制，但叶片的水分流失是不可避免的，因为光合作用需要开放的气孔（即孔隙），通过气孔吸收二氧化碳并损失水蒸气。 因此，在光合作用不活跃的黑暗中，大多数植物预期完全关闭气孔，从而减少水分损失并保存根区中的水分。 然而，与这一预期相反，它已被反复证明，许多植物物种有大量的夜间气孔开放（高达白天值的90%），并在自然条件下有显着的夜间水分损失（高达每日水分损失的15%）。 植物通过高夜间水分损失的水分消耗可能有利于营养有限的植物，至少部分是因为增加了营养供应与水通量的根，如初步数据和计算机模拟所示。 本研究旨在探讨植物夜间气孔开放和失水的适应意义及其调控。 使用实验室，生长室，温室和田间实验三个假设将进行测试。 每一种的实验方法也在下面列出。1）营养物质和水的可用性影响夜间气孔开放和水分损失。 将操纵养分有效性、植物养分状况、土壤和植物水分状况以及大气蒸发需求（例如相对湿度和温度），并将测量对夜间气孔开放的影响。2）在养分比水分更有限的条件下，将发现夜间水分损失对植物生长和种子产量的益处。 通过操纵夜间大气蒸发需求来增加或减少夜间水分损失，并测量对植物养分获取、生长和种子产量的影响。3）在进化尺度上，夜间气孔开度高和水分损失高的选择可能发生在水分丰富但养分有效性低的栖息地。 在相同条件下，评估与不同营养和水分供应的栖息地密切相关的植物物种的夜间气孔开放和水分损失。假设1和2将用四种生长形式和胁迫耐受性不同的重点物种进行测试：鼠耳水芹（小型一年生植物），向日葵（大型一年生植物），油桐（耐盐沙漠灌木）和棉白杨（树）。 这些植物都具有较高的夜间气孔开放度和失水量，但在水分胁迫下，它们可以在夜间进一步关闭气孔。 将测量叶片和整株植物的生理反应以及长期生长和种子产量的影响。 对于假设3，这四个焦点物种将与八个不同分类群中的许多其他物种进行比较，从而对结果进行更广泛的解释。了解夜间失水的影响将为植物如何科普自然界中的水分和养分缺乏提供新的思路。 了解夜间水分损失的程度及其调节对于作物育种和管理非常重要，因为夜间水分损失增加了作物总的用水量。 此外，夜间水分流失及其调节的知识将最终提高对更大尺度过程的理解，如竞争，生态系统水和营养通量，以及植物对气态污染物的吸收。该项目将培养一批多样化的本科生和研究生，一名技术人员和一名博士后研究员。 多诺万和理查兹实验室都有积极招募代表性不足的群体和指导基于调查的本科生研究的良好记录。

Water is a key limiting factor for plant productivity worldwide. Although many mechanisms that reduce water loss have evolved in plants, water loss from leaves is inevitable, since photosynthesis requires open stomata (i.e. pores) through which carbon dioxide is absorbed and water vapor is lost. Accordingly, in the dark when photosynthesis is inactive, most plants are expected to completely close stomata thus reducing water loss and conserving water in the root zone. However, contrary to this expectation, it has been repeatedly demonstrated that many plant species have substantial nighttime stomatal opening (up to 90% of daytime values) and have significant nighttime water loss under natural conditions (up to 15% of daily water loss). Water spending by plants through high nighttime water loss may benefit nutrient-limited plants at least partly because of increased nutrient supply with flux of water to roots, as suggested by preliminary data and computer simulations. The objective of this research is to investigate the adaptive significance and regulation of nighttime stomatal opening and water loss in plants. Using laboratory, growth chamber, greenhouse, and field experiments three hypotheses will be tested. The experimental approach for each is also listed below.1) Availability of nutrients and water affect nighttime stomatal opening and water loss. Nutrient availability, plant nutrient status, soil and plant water status, and atmospheric evaporative demand (e.g. relative humidity and temperature) will be manipulated and effects on nighttime stomatal opening will be measured.2) Benefits of high nighttime water loss for plant growth and seed yield will be found in conditions where nutrients are more limiting than water. Nighttime water loss will be increased or decreased by manipulating atmospheric evaporative demand at night and effects on plant nutrient acquisition, growth, and seed yield will be measured.3) At the evolutionary scale, selection for high nighttime stomatal opening and water loss may have occurred in habitats with abundant water but low nutrient availability. Closely related plant species native to habitats with differing nutrient and water availability will be assessed for nighttime stomatal opening and water loss under uniform conditions.Hypotheses 1 and 2 will be tested with four focal species that differ in growth form and stress tolerance: mouse-ear cress (small annual), sunflower (large annual), greasewood (salt-tolerant desert shrub), and cottonwood (tree). These plant species all have high nighttime stomatal opening and water loss, but they can further close stomata at night under water stress. Leaf and whole-plant physiological responses and long-term growth and seed yield effects will be measured. For Hypothesis 3, the four focal species will be compared to many additional species within eight diverse taxonomic groups allowing broader interpretation of results.Understanding effects of nighttime water loss will shed new light on how plants cope with water and nutrient deficiencies in nature. Knowledge of the magnitude of nighttime water loss and its regulation is important for crop breeding and management, because nighttime water loss increases total crop water use. Additionally, knowledge of nighttime water loss and its regulation will ultimately improve understanding of larger scale processes such as competition, ecosystem water and nutrient fluxes, and uptake of gaseous pollutants by plants. The project will train a diverse group of undergraduate and graduate students, a technician, and a postdoctoral researcher. The Donovan and Richards labs both have strong records of proactively recruiting underrepresented groups and directing inquiry-based undergraduate research.