RAPID: Collaborative Research: What are the Mechanisms of Tree Recovery after an Extreme Episodic Drought?

2011年德克萨斯州、俄克拉何马州和新墨西哥州东部的干旱是自1895年有气象记录以来该地区最严重的一年干旱，也可能是1200多年来最严重的一年干旱。这场干旱持续了2014年，2011至2014年间，德克萨斯州有5亿棵树死亡。对干旱期间树木的研究记录了几个研究地点的个体死亡、光合作用和水分利用的模式。这个项目考察了这些相同的景观和树木如何应对干旱的缓解。得克萨斯州中部从2011年8月的极端干旱到2015年7月的基本没有干旱，这是有记录以来最潮湿的春季和初夏时期之一。这提供了一个独特的“自然实验”，用来检验与抗旱和抗旱恢复有关的那些植物性状的假说。需要检验的一个基本假设是，在干旱期间能够保持较高光合作用的物种将比那些无法保持光合作用的物种恢复得更快(即保持更大的光合作用并表现出更大的生长)。由于在不久的将来会预测到更极端和周期性的气候模式，这项研究将有助于理解植被将如何应对可用水的极端变化。这些信息将对土地管理者特别有用，以确保植被的存在和维持植被提供的生态系统服务。该项目还包括对本科生和博士后进行植物胁迫研究的培训。预计未来间歇性干旱的频率和强度将会增加，这些模式已经在过去15年中观察到。然而，关于在严重干旱中幸存下来的自然生长的树木发生了什么生理变化的信息很少。德克萨斯州中部在2011年经历了有记录以来最严重的一年干旱。这场干旱持续了2014年，估计有5亿棵树死亡。2015年，德克萨斯州中部经历了春末夏初的降雨量，超过了长期平均降雨量的10倍。该地区未来三个月的气候预报是气温低于平均水平，降雨量高于平均水平。这种不同寻常的气候事件组合为研究植被对快速缓解干旱的反应提供了独特的条件。该项目利用的一个主要优势是，研究人员先前对树木对2011-2014年严重干旱的生理和水力传导反应进行了表征。这些相同的个体和地点将被测量生理参数(气体交换、水力参数)、解剖和生长，以允许比较干旱期间和干旱后的测量结果。这些测量将被用来对基于过程的模型进行参数化，以预测这些树在不同水分可用性情景下的碳和水状况。在水资源供应极端变化的情况下，该项目在土地管理和保护森林方面产生了重大而广泛的影响。本科生和博士后助理将直接参与这项研究。这些成果将用于两个参与机构与植物应对环境变化有关的公共宣传。

The 2011 drought in Texas, Oklahoma, and eastern New Mexico was the most severe one-year drought in the region since meteorological record-keeping began in 1895 and potentially the worst single-year drought in over 1200 years. This drought continued through 2014 and killed a half billion trees in Texas between 2011 and 2014. Research on trees during this drought documented patterns of mortality, photosynthesis, and water use for individuals spread across several research sites. This project examines how these same landscapes and trees respond to alleviation of drought. Central Texas has gone from an extreme drought in August of 2011 to essentially no drought in July 2015, due to one of the wettest spring and early summer periods on record. This provides a unique "natural experiment" in which to test hypotheses about those plant traits associated with resistance to drought and recovery from drought. A primary hypothesis to be tested is that species that were able to maintain greater photosynthesis during the drought will recover more quickly (i.e. will maintain greater photosynthesis and will exhibit greater growth) than those species that were unable to maintain photosynthesis. Because more extreme and episodic climate patterns are predicted for the near future, this research will contribute to the understanding of how vegetation will respond to extreme variation in water availability. This information will be particularly useful to land managers to ensure the presence of vegetation and the maintenance of the ecosystem services that vegetation provides. The project also involves training of undergraduate students and postdoctoral associates in plant stress research.The frequency and intensity of episodic droughts are predicted to increase in the future, and these patterns have already been observed over the last 15 years. However, little information exists about what physiological changes occur in naturally-growing trees that survive a severe drought. Central Texas experienced the worst single-year drought in its recorded history in 2011. That drought continued through 2014 and killed an estimated half billion trees. In 2015, Central Texas experienced late spring and early summer rainfall that exceeded long-term averages by 10 times. Climate predictions for the area for the next three months are for below average temperatures and above average rainfall. This unusual combination of climatic events provides a unique situation in which to study vegetation responses to rapid alleviation of drought. A major advantage this project exploits is the previous characterization by the investigators of physiological and hydraulic conductance responses of trees to the severe 2011-2014 drought. These same individuals and sites will be measured for physiological parameters (gas exchange, hydraulic parameters), anatomy, and growth to allow the comparison of measurements taken during and after the drought. The measurements will be used to parameterize a process-based model to predict the carbon and water status of these trees under different moisture availability scenarios. The project has significant broader impacts in land management and conservation of forests under extreme variation in water availability. Undergraduate students will be involved directly in the research, along with postdoctoral associates. The results will be used for public outreach at two of the participating institutions relating plant response to changing environments.