The Role of Soil CO2 Efflux in the Global Carbon Cycle: An Evaluation of Importance and Controls

The global carbon cycle includes biotic and abiotic processes that shape and reshape the face of the Earth. Through a delicate balancing of incoming fluxes of carbon (e.g. photosynthesis) and corresponding outgoing fluxes (e.g. respiration), a dynamic equilibrium has been naturally established for terrestrial systems. In the face of global temperature increases and elevating atmospheric CO 2 , this balance is becoming destabilized. In order to assess the future state of the biosphere, it is necessary to monitor rates of carbon fluxes. One important and easily measured flux is soil respiration, or soil CO 2 efflux. This flux is anticipated to be the component of the carbon budget most sensitive to warming and most likely to see prolonged impacts on the order of centuries. Understanding the controls on this flux of carbon will be important in approaching the issue of future global carbon balance. Soil temperature produces direct fluctuations in rates of soil CO 2 efflux, with effects visible over short as well as long time frames; precipitation, soil moisture, and soil nutrient status are responsible for seasonal and interannual variability in these rates. Additional considerations must be given to environmental aspects, such as topography as well as the biotic community structure in order to encompass a wide range of heterogeneity. Issues of scaling from site-level observations to global predictions are substantial, but further improvements in the available technology utilized in both measurement and analysis of soil CO 2 efflux, as well as the inclusion of more empirical data from unique ecosystems, may lead to a better understanding of soil carbon response to environmental change.

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