RAPID: Woody Plant Responses to Extreme Drought in California: Characterizing Species-Level Drought Survival and Mortality Mechanisms

目前加州的干旱已经进入第四个年头，是加州历史上最干旱的三年记录，该州46%的地区目前处于异常干旱的类别。干旱正在迅速导致全州树木和灌木的大规模死亡，以至于科学家们正在争先恐后地记录对森林和流域的影响。这项研究项目提供了一个研究加州查帕尔灌木与莫哈韦沙漠交界处的乔木和灌木的机会--莫哈韦沙漠是一个植被变化迅速的地区。在这场极端干旱中促进生存的生理和生态特征将被识别出来，并用于预测持续干旱可能如何进一步影响加州的生态系统。这项工作将通过促进森林和流域健康的科学进步来支持NSF的使命，并将具体促进在植物抗旱性、气候变化和自然资源管理方面的研究进展。这项研究将由首席调查员监督，并将利用少数族裔服务机构的本科生和研究生，培训这些学生科学方法、分析和传播结果。该项目的目标是将特定物种的死亡率和存活率与生理机制联系起来，以便能够以预测能力进一步应对加州目前的极端干旱。这项研究将在北美两大生物群加州植物区和莫哈韦沙漠交汇处的一系列永久地块中进行，那里的物种组成有很大潜力因气候变化而发生变化。这些地点所有木本植物的生物地理起源、抗旱性和水力特征已经得到了表征。根据这个社区目前的生理知识，可以实时测量死亡率和实际生理过程之间的联系。该项目还将评估研究物种的生物地理起源的作用，以了解研究系统内局部灭绝和范围收缩的性质。南加州莫龙戈河谷主要研究地点2007年干旱造成的死亡率是存在的，2009年建立了三个0.125公顷的圆形地块，所有木本植物都已确定和标记。长期的永久地块将被重新普查，并将建立另外两个更高海拔的地点，以监测未来的变化。树干测量仪将安装在研究地块内的树干上，以更精细地测量生长对气候的反应。最后，将使用植物木质部水和土壤水的稳定同位素组成的测量来监测水分吸收深度的变化和水源的变化。这项研究将由首席调查员监督，并将在少数族裔服务机构的本科生和研究生的帮助下进行，激发学生对当地生态系统的兴趣。研究区生物多样性强，有大量特有物种。该项目的预期结果是提高预测未来地中海型生态系统中气候变化型干旱持续或加剧时，具有不同干旱应对策略的物种将如何生存的能力，并为学生提供机会处理可能与全球进程相关的关键生态问题。

The current California drought is in its fourth year and represents the driest three-year record in California History, with 46% of the state currently in the category of exceptional drought. The drought is causing mass mortality of trees and shrubs throughout the state so quickly that scientists are scrambling to document the impacts to forests and watersheds. This research project provides an opportunity to study trees and shrubs where the California chaparral shrublands meet the Mojave Desert - an area with rapid changes in vegetation. The physiological and ecological characteristics that promote survival during this extreme drought will be identified and used to predict how continued drought is likely to further affect California ecosystems. The work will support the mission of NSF by promoting the progress of science towards the health of forests and watersheds, and will specifically promote progress in research on plant drought resistance, climate change, and natural resource management. The research will be overseen by the principal investigator, and will utilize undergraduate and graduate students at a minority serving institution, training these students in scientific approaches, analyses, and dissemination of results. The goal of the project is to associate species-specific mortality and survival with physiological mechanisms so that further responses to the current extreme drought in California can be approached with predictive power. The study will be conducted in a series of permanent plots at the intersection of two major North American biomes, the California Floristic Province and the Mojave Desert, where there is great potential for changes in species composition due to climate change. The biogeographical origin, drought resistance, and hydraulic traits of all of the woody species at the sites have already been characterized. Based on the current physiological knowledge of this community, the link between mortality and actual physiological processes can be measured in real time. The project will also allow evaluations of the role of biogeographic origin of study species to understand the nature of local extinction and range contractions within the research system. Mortality rates from the 2007 drought at the primary research location in Morongo Valley in southern California exist, and in 2009 three 0.125 ha circular plots were established, with all woody species identified and marked. Long-term permanent plots will be re-censused, and two additional sites at higher altitudes will be established to monitor future changes. Dendrometer bands will be installed on stems within the research plots for finer scale measurements of growth in response to climate. Finally, measurement of stable isotopic composition of plant xylem water and soil water will be used to monitor changes in the depth of water uptake and changes in water sources. The research will be supervised by the principal investigator and will be conducted with the help of undergraduate and graduate students at a minority serving institution, stimulating student interest in local ecosystems. The study area is highly biodiverse, with large numbers of endemic species. The expected outcome of the project is to increase the ability to predict how species with contrasting drought response strategies will fare as climate change-type drought continues or intensifies in Mediterranean-type ecosystems in the future, and provide opportunities for students to work with critical ecological issues that can be linked to global processes.