Plant physiological response to environmental stress in semiarid ecosystems

由于气候受到破坏，预计下世纪加拿大西部干旱的频率和严重程度将增加。为了保持自然生态系统的活力，我们必须了解不同功能群的植物如何科普有限的水资源。在半干旱生态系统中，乔、灌、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失水的比率。高WUE植物在全日照（Amax）和理想水分条件下的光合速率较低，但在整个夏季干旱期间继续生长。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有机会性，在土壤水分可利用的短暂时期内生长迅速。它们往往有更薄的叶子，含氮量更高，寿命更短。高WUE植物在长寿的树木和木本灌木中比草本灌木和草中更常见，但也有例外，WUE甚至在物种内不同，这是由于水分供应，叶龄，叶在冠层中的位置和雌雄异株植物的性别的季节性变化。我将使用先进的生理生态学技术，包括光合气体交换，叶片反射率，叶绿素荧光，稳定的碳和氢同位素，测量干旱响应功能类型之间的差异，物种之间，性别之间和沿着冠层消光梯度。研究将在阿尔伯塔的河岸林地、针叶林和草地进行。我研究的一个关键焦点是叶肉导度，即二氧化碳在叶腔和叶绿体之间的扩散导度，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，并将应用于更新和保护。学生将接受生态生理学的培训。这项研究有效地解决了NSERC的“健康环境和生态系统”的主题，有针对性地增加资金。

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.