Measuring the Oxidative Ratio of the Terrestrial Biosphere

William Marsh Rice University, Houston TX

Investigators

Abstract

Photosynthesis causes small increases in atmospheric O2 and concomitant small decreases in atmospheric CO2, and decomposition reverses this process. Because the terrestrial biosphere leaves an atmospheric imprint of its activities, fluctuations in atmospheric gases can be used to infer the behavior of the biosphere. Key to interpreting this behavior is the oxidative ratio (OR) of the organic carbon that is created by photosynthesis: that is, the ratio of O2 released to CO2 consumed during photosynthesis. This value is commonly assumed to be about 1.07, but early results show that natural variability in oxidative ratio can be large. Small changes in the terrestrial biosphere's oxidative ratio, on the order of 0.02 units, would cause a major change in our understanding of carbon and oxygen fluxes between the atmosphere, biosphere, and ocean. The goal of this grant is to make the first detailed measurements of an ecosystem's oxidative ratio. Our field site, Kellogg Biological Station in southwest Michigan, contains a series of sites which will allow us to compare ecosystem oxidative ratio over a range of land uses typical of much of the U.S.