Collaborative Research: High Nighttime Stomatal Conductance and Transpiration in Plants

水是全世界植物生产力的关键限制因素。虽然植物已经进化出许多减少水分损失的机制，但叶片的水分损失是不可避免的，因为光合作用需要开放的气孔(即气孔)，二氧化碳通过气孔吸收，水蒸气通过气孔损失。因此，在光合作用不活跃的黑暗中，大多数植物有望完全关闭气孔，从而减少水分损失，保持根区的水分。然而，与这一预期相反的是，人们一再证明，许多植物在夜间有大量的气孔开放(高达白天值的90%)，并在自然条件下有显著的夜间水分损失(高达每日水分损失的15%)。初步数据和计算机模拟表明，植物通过夜间高水分损失进行的水分消耗可能会使营养受限的植物受益，至少部分原因是由于初步数据和计算机模拟表明，随着水分流向根部，养分供应增加。本研究的目的是探讨植物夜间气孔开放和失水的适应意义及其调控。通过实验室、生长室、温室和田间实验，将检验三个假说。每种方法的实验方法如下：1)养分和水分的有效性影响夜间气孔开放和水分损失。将对养分有效性、植物营养状况、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)进行调控，并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，将发现夜间水分大量流失对植物生长和种子产量的好处。通过调节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，选择夜间气孔张开和水分损失可能发生在水分丰富但养分有效性低的生境。假设1和2将用四种生长形式和抗逆性不同的植物进行测试：鼠耳芹(小年生)、向日葵(大年生)、油木(耐盐荒漠灌木)和棉杨(乔木)。这些植物都有较高的夜间气孔张开度和失水率，但在水分胁迫下，它们在夜间可以进一步关闭气孔。将测量叶片和整个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3，四个重点物种将与八个不同分类组中的许多额外物种进行比较，从而允许对结果进行更广泛的解释。理解夜间水分损失的影响将为植物如何应对自然界中的水分和营养缺乏提供新的线索。了解夜间水分损失的大小及其调节对于作物育种和管理非常重要，因为夜间水分损失会增加作物的总用水量。此外，对夜间水分损失及其调节的了解将最终提高对更大范围过程的理解，如竞争、生态系统水和营养通量以及植物对气体污染物的吸收。该项目将培养一批不同的本科生和研究生、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团体和指导基于探究的本科生研究方面都有很好的记录。

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.