Measuring the Oxidative Ratio of the Terrestrial Biosphere

光合作用导致大气中O2的小幅增加和伴随而来的大气CO2的小幅减少，而分解则逆转了这一过程。由于陆地生物圈在大气中留下了其活动的印记，大气气体的波动可以用来推断生物圈的行为。解释这一行为的关键是光合作用产生的有机碳的氧化比率(OR)：即光合作用过程中释放的O2与消耗的CO2的比率。这个值通常被假设为1.07左右，但早期的结果表明，氧化比率的自然变异性可能很大。陆地生物圈氧化比率的微小变化，大约是0.02个单位，将导致我们对大气、生物圈和海洋之间碳和氧通量的理解发生重大变化。这笔赠款的目标是对生态系统的氧化比率进行首次详细测量。我们的野外站点，密歇根州西南部的凯洛格生物站，包含一系列站点，使我们能够比较美国大部分地区典型土地使用情况下的生态系统氧化率。

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.