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Journal Article

The impact of soil microorganisms on the global budget of δ 18O in atmospheric CO2


Cuntz,  M.
Department Biogeochemical Systems, Prof. M. Heimann, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Wingate, L., Ogee, J., Cuntz, M., Genty, B., Reiter, I., Seibt, U., et al. (2009). The impact of soil microorganisms on the global budget of δ 18O in atmospheric CO2. Proceedings of the National Academy of Sciences of the United States of America, 106(52), 22411-22415. doi:10.1073/pnas.0905210106.

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Improved global estimates of terrestrial photosynthesis and respiration are critical for predicting the rate of change in atmospheric CO2. The oxygen isotopic composition of atmospheric CO2 can be used to estimate these fluxes because oxygen isotopic exchange between CO2 and water creates distinct isotopic flux signatures. The enzyme carbonic anhydrase (CA) is known to accelerate this exchange in leaves, but the possibility of CA activity in soils is commonly neglected. Here, we report widespread accelerated soil CO2 hydration. Exchange was 10-300 times faster than the un-catalyzed rate, consistent with typical population sizes for CA-containing soil microorganisms. Including accelerated soil hydration in global model simulations modifies contributions from soil and foliage to the global (COO)-O-18 budget and eliminates persistent discrepancies existing between model and atmospheric observations. This enhanced soil hydration also increases the differences between the isotopic signatures of photosynthesis and respiration, particularly in the tropics, increasing the precision of CO2 gross fluxes obtained by using the delta O-18 of atmospheric CO2 by 50%.