Labile soil carbon inputs mediate the soil microbial community composition and plant residue decomposition rates

Authors

  • Marie-Anne de Graaff,

    1. Department of Biological Sciences, Boise State University, Boise, ID 83725, USA
    2. Molecular Microbial Ecology Group, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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  • Aimee T. Classen,

    1. Department of Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN 37966, USA
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  • Hector F. Castro,

    1. Molecular Microbial Ecology Group, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    2. Department of Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN 37966, USA
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  • Christopher W. Schadt

    1. Molecular Microbial Ecology Group, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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Author for correspondence:
Marie-Anne de Graaff
Tel: +1 208 426 3262
Email: marie-annedegraaff@boisestate.edu

Summary

  • Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities?
  • In a 14 d laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g−1 soil) to soils amended with and without 13C-labeled plant residue. We measured CO2 respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR).
  • Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g−1) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g−1) had no impact on plant residue decomposition, while greater concentrations of C (> 7.2 mg C g−1) reduced decomposition (−50%). Concurrently, high exudate concentrations (> 3.6 mg C g−1) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (< 3.6 mg C g−1) increased metabolic activity rather than gene copy numbers.
  • These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.

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