Plant physiological response to environmental stress in semiarid ecosystems

由于气候破坏，预计下个世纪加拿大西部干旱的频率和严重程度将会增加。为了保持自然生态系统的活力，我们必须了解不同功能组的植物如何应对有限的水供应。在半干旱生态系统中，乔木、灌木和草本植物的耐旱性和避旱策略各不相同。这些差异与水分利用效率(WUE)有关，WUE是叶片通过蒸腾作用获得的光合碳收益与水分损失的比率。高水分利用效率植物在全日照(Amax)和理想的水分条件下具有较低的光合作用速率，但在夏季干旱期间仍能继续生长。它们与具有较高Amax的低WUE植物共存。低水分利用效率的植物更倾向于投机取巧，在土壤水分可利用性的短暂时期内迅速生长。它们的叶片往往更薄，含氮量更高，寿命更短。高WUE植物在长寿乔木和木本灌木中比在草本灌木和草本中更常见，但也有例外，由于水分有效性、叶龄、冠层叶位和雌雄异株植物性别的季节性变化，种内WUE甚至不同。我将使用先进的生态生理学技术，包括光合作用气体交换、叶片反射率、叶绿素荧光和稳定的碳氢同位素，来衡量干旱反应在不同功能型、不同物种、不同性别和不同树冠消光梯度上的差异。研究将在艾伯塔省的河岸林地、针叶林和草原进行。我研究的一个主要焦点是叶肉电导，即二氧化碳在内部叶腔和叶绿体之间的扩散电导，如何影响WUE。我的研究对加拿大很重要，因为它揭示了干旱对半干旱生态系统的生理影响。研究成果将促进对生态系统健康的敏感生理指标的理解，并将被应用于更新和保护。学生将接受生态生理学方面的培训。这项研究有效地解决了NSERC的“健康环境和生态系统”主题，旨在增加资金。

The frequency and severity of drought is expected to increase in western Canada during the next century as a consequence of climate disruption. To maintain the vitality of natural ecosystems, we must understand how different functional groups of plants cope with restricted water availability. Drought tolerance and avoidance strategies vary among tree, shrub and grass species in semiarid ecosystems. These differences are related to water-use efficiency (WUE), the ratio of leaf photosynthetic carbon gain to water loss by transpiration. High WUE plants have lower photosynthesis rates in full sunshine (Amax) and ideal moisture conditions, but continue to grow throughout summer drought. They co-occur with low WUE plants that have higher Amax. Low WUE plants are more opportunistic, growing rapidly during brief periods of soil moisture availability. They tend to have thinner leaves with higher nitrogen content and shorter lifespan. High WUE plants are more common among long-lived trees and woody shrubs than among herbaceous shrubs and grasses, but there are exceptions and WUE even differs within-species, due to seasonal changes in moisture availability, leaf age, leaf position in the canopy and the sex of dioecious plants. I will use advanced ecophysiological techniques, including photosynthetic gas-exchange, leaf reflectance, chlorophyll fluorescence, and stable carbon and hydrogen isotopes, to measure differences in drought response among functional types, among species, between sexes and along a canopy light extinction gradient. Studies will be carried out in riparian woodlands, coniferous forests and grasslands of Alberta. A key focus of my research is how mesophyll conductance, the diffusion conductance of carbon dioxide between internal leaf cavities and chloroplasts, influences WUE. My research is important for Canada, because it reveals physiological impacts of drought in semiarid ecosystems. Research outcomes will advance understanding of sensitive physiological indicators of ecosystem health and will be applied to renewal and conservation. Students will receive training in ecophysiology. This research effectively addresses NSERC's "Healthy Environment and Ecosystems" theme, targeted for increased funding.