The impact of soil microorganisms on the global budget of d super(18)O in atmospheric CO sub(2)

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 52; pp. 22411 - 22415
• Main Authors: Wingate, Lisa, Ogee, Jerome, Cuntz, Matthias, Genty, Bernard, Reiter, Ilja, Seibt, Ulli, Yakir, Dan, Maseyk, Kadmiel, Pendall, Elise G, Barbour, Margaret M, Mortazavi, Behzad, Burlett, Regis, Peylin, Philippe, Miller, John, Mencuccini, Maurizio, Shim, Jee H, Hunt, John, Grace, John
• Format: Journal Article
• Language: English
• Published: 01.01.2009
• ISSN: 0027-8424
• DOI: 10.1073/pnas.0905210106

Improved global estimates of terrestrial photosynthesis and respiration are critical for predicting the rate of change in atmospheric CO sub(2). The oxygen isotopic composition of atmospheric CO sub(2) can be used to estimate these fluxes because oxygen isotopic exchange between CO sub(2) 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 CO sub(2) hydration. Exchange was 10-300 times faster than the uncatalyzed 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 CO super(18)O 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 CO sub(2) gross fluxes obtained by using the d super(18)O of atmospheric CO sub(2) by 50%.