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Mineral protection of soil carbon counteracted by root exudates

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  • Multiple lines of existing evidence suggest that climate change enhances root exudation of organic compounds into soils. Recent experimental studies show that increased exudate inputs may cause a net loss of soil carbon. This stimulation of microbial carbon mineralization ('priming') is commonly rationalized by the assumption that exudates provide a readily bioavailable supply of energy for the decomposition of native soil carbon (co-metabolism). Here we show that an alternate mechanism can cause carbon loss of equal or greater magnitude. We find that a common root exudate, oxalic acid, promotes carbon loss by liberating organic compounds from protective associations with minerals. By enhancing microbial access to previously mineral-protected compounds, this indirect mechanism accelerated carbon loss more than simply increasing the supply of energetically more favourable substrates. Our results provide insights into the coupled biotic-abiotic mechanisms underlying the 'priming' phenomenon and challenge the assumption that mineral-associated carbon is protected from microbial cycling over millennial timescales.
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  • Keiluweit, M., Bougoure, J. J., Nico, P. S., Pett-Ridge, J., Weber, P. K., & Kleber, M. (2015). Mineral protection of soil carbon counteracted by root exudates. Nature Climate Change, 5(6), 588-595. doi:10.1038/nclimate2580
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  • 5
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  • 6
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  • The authors thank A.L.D. Kilcoyne (ALS beamline 5.3.2.2), S.Y. Liu and M. Ahmed (ALS beamline 9.0.2) for their support. M. Keiluweit was supported by a Lawrence Scholar Fellowship awarded through Lawrence Livermore National Laboratory (LLNL). M. Kleber acknowledges support through Research Agreement No. 2014-1918 with the Institute of Soil Landscape Research, Leibniz-Center for Agricultural Landscape Research (ZALF), Muncheberg, Germany. This work was performed under the auspices of the US Department of Energy by LLNL under Contract DE-AC52-07NA27344. Funding was provided by LLNL LDRD 'Microbes and Minerals: Imaging C Stabilization' and a US DOE Genomics Science program award SA-DOE-29318 to J.P-R. The work of P.S.N. is supported by LBNL award No. IC006762 as sub-award from LLNL and DOE-BER Sustainable Systems SFA. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US DOE under Contract No. DE-AC02-05CH11231.
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file details KeiluweitMarcoCropSoilSciMineralProtectionSoil.pdf 07/26/2017 Public
file details KeiluweitMarcoCropSoilSciMineralProtectionSoilSupplementaryInfo.pdf 07/26/2017 Public