The Effects of Land Use Change on the Oxidative Ratio of the Terrestrial Biosphere

生态系统的氧化比（OR）是一个基本的生态特性，定义为每摩尔CO2固定释放的O2净摩尔数。在全球范围内，OR在计算化石燃料CO2在环境中的命运方面发挥着关键作用。计算机模型表明，OR的微小变化可能导致陆地碳汇规模估计值的潜在重大变化。尽管它的意义，只有一个测量生态系统或已出版，和自然变化的OR仍然无法测量。 陆地生物圈的OR季节性地印在大气中，使得有可能通过测量大气中CO2和O2浓度的变化来分配海洋和陆地生物圈之间的碳。陆地生物圈的OR的任何变化都会改变大气中的O2浓度，从而影响陆地/海洋碳汇分配的准确性。当个体生物体将碳固定为更多的氧化或还原形式以应对干旱等环境压力时，以及当植物群落因土地利用变化等外部驱动因素而发生变化时，生态系统OR可能会发生变化。 现在已经证明，可以足够准确和精确地测量自然生物量的OR，以开始在生态系统尺度上工作。研究者还在凯洛格生物站长期生态研究站点的几种土地利用下对生态系统OR进行了初步测量，结果表明，随着土地利用的变化，生态系统OR存在显著差异。在凯洛格的作物系统有较低的OR比森林和混合林草生态系统，指出全球的解释的潜力。这项研究将继续扩大在凯洛格网站的土地利用变化，氮沉降和降水的梯度，并将是第一个记录的生态系统或变化的幅度。一个博士生和一个本科生将在这个项目上工作。PI有将本科生（特别是来自代表性不足的群体的女性）纳入她的研究的历史，主办机构有本科生参与研究的强大历史。该项目将利用赖斯的卓越和教育公平中心，为寻找和指导科学领域代表性不足的学生提供指导。

The oxidative ratio (OR) of an ecosystem is a fundamental ecological property, defined as the net moles of O2 released per mole CO2 fixed. On a global scale, the OR plays a key role in calculations to apportion the fate of fossil fuel CO2 in the environment. Computer models have shown that small changes in OR can cause potentially significant changes in estimates of the size of the terrestrial carbon sink. Despite its significance, only one measurement of ecosystem OR has been published, and natural variation in OR remains unmeasured. The OR of the terrestrial biosphere seasonally imprints the atmosphere, making it possible to apportion carbon between the oceans and the terrestrial biosphere by measuring changes in atmospheric CO2 and O2 concentrations. Any change in the terrestrial biosphere's OR alters the atmosphere's O2 concentration, influencing the accuracy of land/ocean carbon sink apportionment. Ecosystem OR can change when individual organisms fix carbon into more oxidized or reduced forms in response to environmental stresses such as drought, and when plant communities shift because of external drivers such as land use change. It has been demonstrated now that the OR of natural biomass can be measured with sufficient accuracy and precision to start working at ecosystem scales. The investigator has also made preliminary measurements of ecosystem OR under a few land uses at the Kellogg Biological Station Long-Term Ecological Research site, which show significant variation with land use. Crop systems at Kellogg have lower ORs than forested and mixed forest-grass ecosystems, pointing to the potential for global interpretations. This research will continue and be expanded at the Kellogg site across gradients of land use change, nitrogen deposition, and precipitation, and will be the first to document the magnitude of variations in ecosystem OR.One PhD student and an undergraduate student will work on this project. The PI has a history of incorporating undergraduates (especially women from underrepresented groups) into her research, and the host institution has a strong history of undergraduate participation in research. This project will tap into Rice's Center for Excellence and Equity in Education for guidance in finding and mentoring underrepresented students in the sciences.