Collaborative Research: High Nighttime Stomatal Conductance and Transpiration in Plants

水是世界范围内植物生产力的一个关键限制因素。虽然植物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（即气孔），通过气孔吸收二氧化碳并损失水蒸气。因此，在黑暗中，当光合作用不活跃时，大多数植物有望完全关闭气孔，从而减少水分损失，保持根区水分。然而，与这一预期相反，已经反复证明，许多植物物种具有大量的夜间气孔开度（高达白天值的90%），并且在自然条件下具有显著的夜间失水（高达每日失水的15%）。正如初步数据和计算机模拟所表明的那样，植物通过夜间大量失水而消耗的水分至少在一定程度上有利于营养有限的植物，因为水分流入根部增加了营养供应。本研究的目的是探讨夜间植物气孔开放和水分流失的适应意义和调控。采用实验室、生长室、温室和田间实验对三个假设进行验证。每种方法的实验方法也列在下面。1)养分和水分的有效性影响夜间气孔开放和水分流失。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（如相对湿度和温度）将被控制，并将测量对夜间气孔开放的影响。2)在营养比水分更有限的条件下，夜间高失水对植物生长和种子产量的好处将被发现。通过控制夜间大气蒸发需求，可以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流失的选择可能发生在水分充足但养分利用率低的生境。在均匀的条件下，将评估不同营养和水分可用性栖息地的近缘植物物种的夜间气孔开放和水分损失。假设1和2将用四种不同生长形式和抗逆性的焦点物种进行测试：鼠耳草（小型一年生植物）、向日葵（大型一年生植物）、油木（耐盐沙漠灌木）和棉木（乔木）。这些植物在夜间都有较高的气孔开度和水分损失，但在水分胁迫下，它们可以在夜间进一步关闭气孔。将测量叶片和整个植株的生理反应以及长期生长和种子产量的影响。对于假设3，四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，从而允许更广泛的解释结果。了解夜间水分流失的影响将有助于了解植物如何应对自然界中水分和营养的缺乏。了解夜间失水的严重程度及其调控对作物育种和管理很重要，因为夜间失水增加了作物的总用水量。此外，了解夜间水分流失及其调节将最终提高对更大规模过程的理解，如竞争、生态系统水和养分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。多诺万和理查兹的实验室在积极招募代表性不足的群体和指导基于探究的本科生研究方面都有良好的记录。

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.