Using carbon oxidation state and ecosystem oxidative ratio to understand terrestrial ecosystem response to elevated CO2

Abstract:

Here we show that an easily-measured biogeochemical tracer, carbon oxidation state (C_ox) can be used to understand ecosystem response to elevated atmospheric CO₂ concentrations. We briefly review the use of C_ox in understanding C sink estimates, and its role in understanding the coupled nature of carbon and oxygen cycles, which derives from its relationship with ecosystem oxidative ratio (OR). The C_ox of a carbon pool provides an integrated measure of all processes that create and destroy organic matter (e.g. photosynthesis, respiration, fire) and therefore, can be used to estimate the oxidative ratio (O₂/CO₂) of biosphere-atmosphere exchange. Our preliminary data suggest that the OR of temperate hardwood forest and grassland ecosystems are influenced by atmospheric CO₂ concentration. The variation in ecosystem C_ox with atmospheric CO₂ concentration suggest that OR is not a conservative property of terrestrial ecosystems on annual or decadal timescales. In the grassland ecosystem, the C_ox of plant biomass increased by as much as 50% across a CO₂ concentration gradient of 190 ppm, but the response was highly dependent upon soil properties. In the temperate forest, the C_ox of the soil C pool increased by 40% after 9 seasons of CO₂ enrichment (by 175 ppm). We will discuss our interpretation of C_ox as a proxy and its potential use in studies of coupled O₂ and CO₂ cycling.