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Title: Mineral protection of soil carbon counteracted by root exudates [Root exudates counteract mineral control on soil carbon turnover]

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. Lastly, 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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5]
  1. Oregon State Univ., Corvallis, OR (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Western Australia, Western Australia (Australia)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Oregon State Univ., Corvallis, OR (United States); Leibnitz-Zentrum fur Agrarlandschaftsforschung (ZALF), Muncheberg (Germany)
Publication Date:
OSTI Identifier:
1313557
Report Number(s):
LLNL-JRNL--644153
Journal ID: ISSN 1758-678X
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Nature Climate Change
Additional Journal Information:
Journal Volume: 5; Journal Issue: 6; Journal ID: ISSN 1758-678X
Publisher:
Nature Publishing Group
Research Org:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; 59 BASIC BIOLOGICAL SCIENCES