Water Balance and Plant Ecophysiology in Coastal California: Linking Models and Mechanisms to Project Winners and Losers under Future Climate Scenarios

动植物物种的地理分布范围与环境条件密切相关，包括温度和降雨的季节性模式。在加州，几乎所有的雨水都是在冬天下的，植物在炎热干燥的夏季经历了严重的缺水。夏季旱季对不同物种的影响可能非常不同，这取决于它们的根长到多深才能获得水，以及耐旱程度的差异。了解这些因素如何在景观中变化对于理解和预测树木对温暖干燥气候的脆弱性至关重要。该项目将解决加州橡树林地树种的这一重要问题，目前加州橡树林地正经历着四年来的严重干旱。树木的同位素和生理测量将与一个景观尺度模型相结合，该模型捕捉气候和土壤对缺水的影响。通过将这两种方法结合起来，它将提高预测不同气候条件如何影响不同地理范围内树种的表现，以及它们对温暖和干燥条件的脆弱性的能力。该项目还将在几个职业阶段向年轻专业人员提供培训，包括从代表性不足的群体招聘本科助理。物种沿环境梯度分布的研究是生态学研究的核心，对预测物种对快速变化的环境的反应起着关键作用。本项目探讨了加州橡树林地树种对缺水时空变化响应的生理机制。一个中心目标是了解物种在景观位置、生根深度和气孔生理调节（等水与各向异性）方面的差异如何影响季节性缺水的强度，以及对未来更温暖、更干燥气候的脆弱性的影响。将在四个地点研究八种树种，这些地点跨越温度、降水和气候水平衡的梯度。氧同位素和黎明前水势将用于评估功能生根深度。比较水力策略，包括木质部对栓塞的脆弱性和叶片水分关系的测量，将捕捉物种对旱季水分不足的反应。研究结果将被整合到一个高分辨率、景观尺度的水平衡模型中，以开发新的预测，即在不同的气候条件下，水短缺将如何影响不同水力策略的物种。这些校准的模型将进一步与对未来环境的预测相结合，以产生物种对环境变化脆弱性的机制预测。该项目的成果将通过与区域非政府组织的合作，直接纳入当地的保护规划和资源管理。培养1名博士后和若干名研究生；本科研究助理将通过伯克利学者计划（Berkeley Scholars Program）和Pepperwood Preserve与圣罗莎初级学院（Santa Rosa Junior College）的合作计划招聘。伯克利学者计划是一个获奖项目，支持来自代表性不足群体的学生的研究和职业发展。圣罗莎初级学院是一家位于主要现场附近的西班牙裔服务机构。

The geographic ranges of plant and animal species are closely tied to environmental conditions, including the seasonal patterns of temperature and rainfall. In California, almost all rain falls in winter, and plants experience severe water deficits during the hot, dry summer months. The summer dry season can have very different effects on different species, depending on how deep their roots grow to access water and differences in the degree of drought tolerance. Understanding how these factors vary across a landscape is critical to understand and predict the vulnerability of trees to a warmer and drier climate. This project will address this important problem in tree species of California oak woodlands, currently experiencing a severe, four-year drought. Isotopic and physiological measurements of trees will be combined with a landscape scale model that captures the effects of climate and soils on water deficits. By connecting these two approaches it will improve the ability to predict how different climatic conditions will impact the performance of tree species in different parts of their geographic range, and their vulnerability to warmer and drier conditions. The project will also provide training to young professionals at several career stages, including recruitment of undergraduate assistants from under-represented groups.The study of species distributions along environmental gradients is central to ecological research, and plays a critical role projecting species responses to a rapidly changing environments. This project addresses the physiological mechanisms underlying the responses of tree species in California oak woodlands to spatial and temporal variability in water deficits. A central goal is to understand how species differences in landscape position, rooting depth and the physiological regulation of stomata (isohydry vs. anisohdry) influence the intensity of seasonal water deficits, and the implications for vulnerability to a warmer, drier future climate. Eight tree species will be studied across four sites that span gradients of temperature, precipitation and climatic water balance. Oxygen isotopes and predawn water potentials will be used to assess functional rooting depth. Comparative hydraulic strategies, including measures of xylem vulnerability to embolism and leaf water relations, will capture species' responses to dry season water deficits. The results will be integrated into a high-resolution, landscape-scale water balance model to develop novel projections of how water deficits will impact species with different hydraulic strategies in responses to varying climatic conditions. These calibrated models will be further combined with projections of future environments to generate mechanistic predictions of species vulnerability to environmental change. The results of this project will be directly incorporated into local conservation planning and resource management, through collaborations with regional NGOs. Training will be provided for one post-doc and several graduate students; undergraduate research assistants will be recruited through the Berkeley Scholars Program, an award winning program supporting research and career development for students from under-represented groups, and through Pepperwood Preserve's collaborative programs with the Santa Rosa Junior College, an Hispanic-Serving Institution located close to the primary field site.