Ecological Interpretation of Hydrogen and Oxygen Isotope Ratios in Tree-Ring Cellulose

9508671降水的季节和区域模式与植物对这些水输入的利用之间的关系在若干水平和时间尺度上具有基本和应用的意义。确定能够对植物的特定用水模式（即降水与地下水的利用）提供定量评估的测量方法，将对理解这种关系作出重大贡献。这项研究将检验这样一种假设，即对木材中自然水平的氢和氧同位素进行稳定同位素比率分析，将在短期和长期尺度上提供这一信息。其目标是开发、测试和应用影响树木年轮中纤维素同位素比率的因素的定量模型。树木年轮信息将允许重建树木生长季节的季节性和年度用水模式和湿度条件。该模型将通过使用美国西部常见的四种树木进行实验室实验来开发。由于水源和湿度条件不同，将在选定的地点通过实地观察进行测试。然后，该模型将用于重建犹他州四种植物从幼苗建立到成熟的水分利用历史（降水与地下水）、大气湿度（叶片与空气的梯度）和相对水分利用效率（通过碳同位素判别）。一旦树木年轮同位素比率的定量机制模型被开发出来，它们就可以应用于揭示整个景观的季节性降水的历史模式，对水分来源和湿度变化的生理过程的敏感性，以及有助于树木群落结构长期变化的水关系方面。这项研究将允许从个体到景观水平的生理参数的缩放，并将提供生理学和生物圈-大气相互作用的全球水平研究之间的直接联系。

9508671 The relationship between seasonal and regional patterns of precipitation and the use of those water inputs by plants has ramifications at several levels and time scales that are of both basic and applied interest. Identification of measurements that can provide quantitative assessment of specific water use patterns (that is, use of precipitation versus groundwater) by plants would make a major contribution to understanding that relationship. This research will test the hypothesis that stable isotope ratio analysis of hydrogen and oxygen isotopes at natural levels in wood will provide that information, at both short-term and long-term scales. Its goal is to develop, test, and apply quantitative models of the factors that influence isotope ratios of cellulose in tree rings. The tree ring information will allow reconstruction of seasonal and annual patterns of water use and humidity conditions during the growing season over the life of the tree. The model will be developed through laboratory experiments using four species of trees common in the western United States. It will be tested through field observations at sites chosen because they differ in water sources and humidity conditions. The model will then be used to reconstruct the history of water use (precipitation versus ground water), atmospheric humidity (leaf to air gradients) and relative water use efficiency (through carbon isotope discrimination) by the four species in Utah from seedling establishment through maturity. Once quantitative, mechanistic models of tree- ring isotope ratios are developed, they can be applied to unraveling historic patterns of seasonal precipitation across the landscape, sensitivity of physiological processes to changes in moisture sources and humidity, and aspects of water relations that contribute to the long-term changes in tree community structure. This r esearch will allow for scaling of physiological parameters from individual to landscape levels and will provide a direct link between physiology and global-level studies of biosphere-atmosphere interactions.