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.
