Acclimation of plants and ecosystems to warmer temperatures and altered precipitation

人类活动正在增加大气中的二氧化碳，造成气温升高和降水模式改变等后果。一些模型表明，更温暖和更干燥的条件将导致生态系统释放更多的二氧化碳，对大气和进一步的气候变化做出积极的反馈。然而，这种潜在的正反馈的大小和控制它的机制是全球变化科学中尚未解决的主要问题。我的研究计划的一个长期目标是更好地了解控制植物和生态系统如何对变暖的温度和变化的降水做出反应和适应的生理机制。特别是，我研究了植物和生态系统中的光合作用和呼吸作用，这些过程决定了生态系统是二氧化碳的净源还是汇。我提议启动一系列新的实验，单独和联合研究植物和生态系统对实验性变暖和降水操纵的反应和适应。这些实验和分析将在本地混合草地草原生态系统中进行。草原生态系统为研究植物和生态系统生理学提供了特殊的机会，因为在这些系统中，生长季节和研究年间可能发生广泛的环境条件和植物反应。该提案定义了四个短期目标，为学生研究项目提供了一个框架。第一个目标是验证这样一个假设，即温度升高会增加根部的碳排放，从而刺激微生物的呼吸和旧土壤有机质的分解，向大气中释放二氧化碳。第二个目标将检验这一假设，即较高的温度，特别是与高太阳辐射暴露相关的温度，会刺激植物的呼吸，因为在胁迫条件下，电子分配转移到替代途径的呼吸。在过去的50年里，夜间气温的上升速度是白天气温的1.4倍。这种不对称的昼夜变暖是影响生态系统的一种未得到充分认识的气候特征。第三个目标是确定白天和夜间变暖对生态系统生产力的潜在相反影响的后果。即使年总降雨量没有变化，降雨事件的强度和时间的变化也会对植物和土壤的生理过程产生重大影响。第四个目标将检验这一假设，即尽管降雨事件之间的干旱时间较长，但气温变暖与更大的降雨事件相互作用，以刺激更高的植物生产力和土壤微生物活动。这些研究的数据将与定量模型的预测进行比较，以进一步了解植物和生态系统对环境变化的观察到的生理反应的机制控制和原因。最后，这些研究产生的新的生理信息将被用于改进预测和评估全球环境变化对植物和生态系统生理学影响的模型。

Human activities are increasing atmospheric carbon dioxide with consequences such as warmer air temperatures and altered precipitation patterns. Some models suggest that warmer and drier conditions will result in an increased release of carbon dioxide from ecosystems, contributing a positive feedback to the atmosphere and further climate change. However, the magnitude of this potential positive feedback and the mechanisms controlling it represent major unsolved problems in global change science. A long-term objective of my research program is to better understand the physiological mechanisms that control how plants and ecosystems respond and acclimate to warmer temperatures and altered precipitation. In particular, I study photosynthesis and respiration in plants and ecosystems, and these processes determine whether ecosystems are net sources or sinks of carbon dioxide. I propose to initiate a new series of experiments to investigate the response and acclimation of plants and ecosystems to experimental warming and precipitation manipulation, alone and in combination. These experiments and analyses will be conducted in a native, mixed grass prairie ecosystem. Grassland ecosystems offer special opportunities to study plant and ecosystem physiology because of the wide range of environmental conditions and plant responses that can occur within growing seasons and among study years in these systems. The proposal defines four short-term objectives that provide a framework for student research projects. The first objective is to test the hypothesis that warmer temperatures increase carbon exudation by roots, which subsequently stimulates microbial respiration and the breakdown of old soil organic matter, releasing carbon dioxide to the atmosphere. A second objective will examine the hypothesis that higher temperature, particularly in association with exposure to high solar radiation, stimulates plant respiration because of a shift in electron partitioning to the alternative pathway respiration under stressful conditions. Over the last 50 years, nighttime temperatures have increased 1.4 times faster than daytime temperatures. This asymmetric, day-night warming is an under-appreciated climate characteristic affecting ecosystems. A third objective is to determine the consequences of the potential opposing effects of daytime and nighttime warming on ecosystem productivity. Changes in the intensity and timing of rainfall events, even without changes in the annual precipitation total, can have significant effects on plant and soil physiological processes. The fourth objective will test the hypothesis that warmer temperatures interact with larger rainfall events to stimulate higher plant productivity and soil microbial activity, despite longer dry periods between rainfall events. Data from these studies will be compared to the predictions of quantitative models to gain further understanding of the mechanistic controls and the reasons for the observed physiological responses of plants and ecosystems to the environmental changes. Finally, the new physiological information generated from these studies will be used to improve models that predict, and help to evaluate, the consequences of global environmental changes for plant and ecosystem physiology.