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Plant rhizosphere influence on microbial C metabolism: the role of elevated CO2, N availability and root stoichiometry

Abstract

Microbial decomposer C metabolism is considered a factor controlling soil C stability, a key regulator of global climate. The plant rhizosphere is now recognized as a crucial driver of soil C dynamics but specific mechanisms by which it can affect C processing are unclear. Climate change could affect microbial C metabolism via impacts on the plant rhizosphere. Using continuous 13C labelling under controlled conditions that allowed us to quantify SOM derived-C in all pools and fluxes, we evaluated the microbial metabolism of soil C in the rhizosphere of a C4 native grass exposed to elevated CO2 and under variation in N concentrations in soil and in plant root C:N stoichiometry. Our results demonstrated that this plant can influence soil C metabolism and further, that elevated CO2 conditions can alter this role by increasing microbial C efficiency as indicated by a reduction in soil-derived C respiration per unit of soil C-derived microbial biomass. Moreover, under elevated CO2 increases in soil N, and notably, root tissue N concentration increased C efficiency, suggesting elevated CO2 shifted the stoichiometric balance so N availability was a more critical factor regulating efficiency than under ambient conditions. The root C:N stoichiometry effect indicates that plant chemical traits such as root N concentration are able to influence the metabolism of soil C and that elevated CO2 conditions can modulate this role. Increased efficiency in soil C use was associated with negative rhizosphere priming and we hypothesize that the widely observed phenomenon of rhizosphere priming may result, at least in part, from changes in the metabolic efficiency of microbial populations. Observed changes in the microbial community support that shifting microbial populations were a contributing factor to the observed metabolic responses. Our case study points at greater efficiency of the SOM-degrading populations in a high CO2, high N world, potentially leading to greater C storage of microbially assimilated C in soil.

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Acknowledgments

We thank Jennifer Bell, Courtney Ellis, Joanne Newcomb, Lyndsy Soltau, Janet Chen, Jana Heisler-White, Marcus Brock and Matthew Rubin for assistance in the field and in the laboratory. This material is based upon work supported by the University of Wyoming through a Grant-in-Aid of Research, National Science Foundation (Grant No. 1021559 DEB), USDA-CSREES Soil Processes Program (Grant No. 2008-35107-18655), US Department of Energy’s Office of Science (BER) through the Terrestrial Ecosystem Science program, the Western Regional Center of the National Institute for Climatic Change Research at Northern Arizona University, and by the Australian Research Council (FT100100779). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Correspondence to Yolima Carrillo.

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Responsible Editor: Matthew David Wallenstein.

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Carrillo, Y., Dijkstra, F.A., Pendall, E. et al. Plant rhizosphere influence on microbial C metabolism: the role of elevated CO2, N availability and root stoichiometry. Biogeochemistry 117, 229–240 (2014). https://doi.org/10.1007/s10533-014-9954-5

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  • DOI: https://doi.org/10.1007/s10533-014-9954-5

Keywords

  • Elevated CO2
  • Microbial efficiency
  • Carbon
  • Soil organic matter
  • Microbial communities
  • Metabolic quotient
  • Nitrogen
  • Stoichiometry
  • Roots