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

2011年发生在德克萨斯州、俄克拉荷马州和新墨西哥州东部的干旱是该地区自1895年开始气象记录以来最严重的一年干旱，也可能是1200多年来最严重的一年干旱。这场干旱持续到2014年，在2011年至2014年期间，德克萨斯州有5亿棵树死亡。在干旱期间对树木的研究记录了几个研究地点的树木死亡率、光合作用和水分利用模式。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。德克萨斯州中部从2011年8月的极度干旱到2015年7月的基本无干旱，这是有记录以来最潮湿的春季和初夏之一。这提供了一个独特的“自然实验”，可以测试与抗旱和抗旱恢复有关的植物性状的假设。要验证的一个主要假设是，在干旱期间能够保持更大的光合作用的物种将比那些不能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快的生长）。由于预计在不久的将来会出现更多的极端和偶发性气候模式，因此这项研究将有助于了解植被如何应对水分供应的极端变化。这些资料对土地管理人员确保植被的存在和维持植被提供的生态系统服务特别有用。该项目还包括培养植物胁迫研究方面的本科生和博士后。预计未来偶发性干旱的频率和强度将增加，过去15年来已经观察到这些模式。然而，关于在严重干旱中生存的自然生长的树木发生了什么生理变化的信息很少。2011年，德克萨斯州中部经历了有记录以来最严重的单年干旱。这场干旱持续到2014年，估计有5亿棵树死亡。2015年，德克萨斯州中部春末夏初的降雨量超过了长期平均水平的10倍。该地区未来三个月的气候预测是气温低于平均水平，降雨量高于平均水平。这种不寻常的气候事件组合为研究植被对干旱快速缓解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之前对树木对2011-2014年严重干旱的生理和水力传导反应的描述。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，以便在干旱期间和之后进行测量比较。这些测量结果将用于参数化一个基于过程的模型，以预测这些树木在不同水分可用性情景下的碳和水状况。该项目对土地管理和在水资源极端变化的情况下保护森林具有重大的广泛影响。本科生和博士后将直接参与研究。研究结果将用于两个参与机构有关植物对环境变化的反应的公众宣传。

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.