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

2011年德克萨斯州、俄克拉荷马州和新墨西哥州东部的干旱是该地区自1895年有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。在这场干旱中对树木的研究记录了分布在几个研究地点的死亡率，光合作用和个人用水的模式。该项目研究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月的极端干旱到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时期之一。这提供了一个独特的“自然实验”，在其中测试有关这些植物性状与抗旱性和干旱恢复的假设。需要检验的一个主要假设是，在干旱期间能够保持更大光合作用的物种将比那些不能保持光合作用的物种更快地恢复（即将保持更大的光合作用，并将表现出更大的增长）。由于预测在不久的将来会出现更多极端和偶发的气候模式，这项研究将有助于了解植被如何应对水资源的极端变化。这一信息将特别有助于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。该项目还涉及对本科生和博士后研究人员进行植物胁迫研究方面的培训，预计未来间歇性干旱的频率和强度将增加，过去15年来已经观察到了这些模式。然而，关于在严重干旱中幸存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年经历了有史以来最严重的一年干旱。干旱持续到2014年，估计有5亿棵树死亡。2015年，德克萨斯州中部经历了春末夏初的降雨量，超过长期平均值的10倍。该地区未来三个月的气候预测是低于平均气温和高于平均降雨量。这种不寻常的气候事件组合提供了一个独特的情况下，研究植被迅速缓解干旱的反应。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的表征。这些相同的个人和网站将测量生理参数（气体交换，水力参数），解剖学和生长，以便比较干旱期间和之后采取的测量。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供应情况下的碳和水状况。该项目在水资源极端变化的情况下对土地管理和森林保护产生了广泛的重大影响。本科生将直接参与研究，沿着博士后同事。研究结果将用于两个参与机构的公众宣传，使植物对不断变化的环境作出反应。

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.