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分供应。在半干旱生态系统中，乔木、灌木和禾草物种的耐旱和避旱策略各不相同。这些差异与水分利用效率（WUE）有关，即叶片光合碳增益与蒸腾水分损失的比率。高水分利用效率的植物在充分日照（Amax）和理想水分条件下的光合作用速率较低，但在夏季干旱时仍能继续生长。它们与具有较高Amax的低WUE植物共存。水分利用效率低的植物更具机会性，在土壤水分可利用性较短的时期内生长迅速。它们的叶片往往较薄，含氮量较高，寿命较短。与草本灌木和禾草植物相比，高水分利用效率植物在长寿乔木和木本灌木中更为常见，但由于水分有效性、叶龄、叶片在冠层中的位置和雌雄异株植物性别的季节变化，也存在例外，WUE甚至在物种内也存在差异。我将使用先进的生态生理学技术，包括光合气体交换、叶片反射率、叶绿素荧光和稳定的碳和氢同位素，来测量不同功能类型、物种、性别和冠层光消退梯度之间干旱响应的差异。研究将在艾伯塔省的河岸林地、针叶林和草原上进行。我研究的一个重点是叶肉电导，即二氧化碳在叶腔和叶绿体之间的扩散电导，如何影响水分利用效率。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敏感生理指标的认识，并将应用于生态系统的更新和保护。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，目标是增加资金。

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.