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

一个生态系统的氧化比（OR）是一个基本的生态特性，定义为每摩尔固定的二氧化碳释放的净摩尔O2。在全球范围内，OR在计算化石燃料二氧化碳在环境中的命运时起着关键作用。计算机模型表明，OR的微小变化可能导致对陆地碳汇大小的估计发生潜在的重大变化。尽管具有重要意义，但仅发表了一种生态系统OR的测量方法，并且仍然无法测量OR的自然变化。陆地生物圈的OR季节性地在大气中留下印记，从而可以通过测量大气中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。当个体生物将碳固定为更氧化或更还原的形式以响应干旱等环境压力时，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就会发生变化。现在已经证明，可以以足够的准确度和精度测量天然生物量的OR，从而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对几种土地利用方式下的生态系统OR进行了初步测量，结果显示不同土地利用方式下的生态系统OR存在显著差异。凯洛格的作物系统比森林和森林-草混合生态系统的ORs要低，这表明了全球解释的潜力。这项研究将在凯洛格站点继续进行并扩展，跨越土地利用变化、氮沉积和降水的梯度，并将首次记录生态系统OR变化的幅度。一名博士生和一名本科生将参与这个项目。PI有将本科生（尤其是来自代表性不足群体的女性）纳入其研究的历史，而主办机构在本科生参与研究方面有着悠久的历史。该项目将利用莱斯大学教育卓越与公平中心的指导，寻找和指导科学领域代表性不足的学生。

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.