Bad News for Soil Carbon Sequestration?

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Science  31 Aug 2012:
Vol. 337, Issue 6098, pp. 1049-1050
DOI: 10.1126/science.1227303

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Rising atmospheric carbon dioxide (CO2) concentrations are expected to increase plant photosynthetic activity and the transfer of fixed carbon belowground, providing a potential buffering mechanism against elevated CO2 (1). Arbuscular mycorrhizal fungi (AMF) are central to this potential extra carbon sequestration. AMF form symbioses with most land plants, in which the fungi supply the plant with nutrients in exchange for carbohydrates (2, 3). But to what extent will this extra fixed carbon stay sequestered in the soil (1)? On page 1084 of this issue, Cheng et al. (4) show not only that the extra soil carbon is respired back to the atmosphere, but also that AMF activity stimulates additional decomposition of soil organic carbon. Increased carbon fixation by plants and transport of this carbon to the soil via AMF may thus result in a net source of CO2, rather than the sink we might have hoped for.