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The effects of tree rhizodeposition on soil exoenzyme activity, dissolved organic carbon, and nutrient availability in a subalpine forest ecosystem

  • Ecosystem Ecology
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Abstract

Previous studies have found that root carbon inputs to the soil can stimulate the mineralization of existing soil carbon (C) pools. It is still uncertain, however, whether this “primed” C is derived from elevated rates of soil organic matter (SOM) decomposition, greater C release from microbial pools, or both. The goal of this research was to determine how the activities of the microbial exoenzymes that control SOM decomposition are affected by root C inputs. This was done by manipulating rhizodeposition with tree girdling in a coniferous subalpine forest in the Rocky Mountains of Colorado, USA, and following changes in the activities of nine exoenzymes involved in decomposition, as well as soil dissolved organic C, dissolved organic and inorganic nitrogen (N), and microbial biomass C and N. We found that rhizodeposition is high in the spring, when the soils are still snow-covered, and that there are large ephemeral populations of microorganisms dependent upon this C. Microbial N acquisition from peptide degradation increased with increases in microbial biomass when rhizodeposition was highest. However, our data indicate that the breakdown of cellulose, lignin, chitin, and organic phosphorus are not affected by springtime increases in soil microbial biomass associated with increases in rhizodeposition. We conclude that the priming of soil C mineralization by rhizodeposition is due to growth of the microbial biomass and an increase in the breakdown of N-rich proteins, but not due to increases in the degradation of plant litter constituents such as cellulose and lignin.

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Acknowledgments

Thanks to the Niwot Ridge LTER program for providing measurement support for the inorganic N analyses. We thank Dr. Bill Bowman (University of Colorado Mountain Research Station) for providing valued logistical support in establishing the girdled and nongirdled plots. This work was financially supported by a grant from the South-Central Section of the National Institute for Global Environmental Change (NIGEC) through the US Department of Energy (BER Program) (Cooperative Agreement No. DE-FC03-90ER61010), and grants from the US National Science Foundation’s Ecological and Evolutionary Physiology (IBN-0212267) and Microbial Observatories (MCB-0455606) programs. We thank Laura Brotherton, Sean Burns, Peter Casey, Eric Reinsvold, and Lisa Tiemann for assistance in the field and lab. We would also like to thank Robert Sinsabaugh, Christian Lauber, and Marcy Gallo for assistance with the enzyme assays, and Jason Neff and Jon Carrasco for assistance with the DOC and DON analyses. We are also grateful for Bruce Caldwell's help in reviewing this manuscript and providing valuable input on table 1. Climate data were provided by the Niwot Ridge Long-Term Ecological Research project (NSF DEB 0423662) and the Mountain Research Station (BIR 9115097).

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Authors and Affiliations

  1. Department of Environmental Sciences, University of Toledo, 2801 W. Bancroft Street, Mail Stop 604, Toledo, OH, 43606, USA

    Michael N. Weintraub

  2. Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA

    Laura E. Scott-Denton, Steven K. Schmidt & Russell K. Monson

  3. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, 80309, USA

    Russell K. Monson

Authors
  1. Michael N. Weintraub
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  2. Laura E. Scott-Denton
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  3. Steven K. Schmidt
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  4. Russell K. Monson
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Correspondence to Michael N. Weintraub.

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Communicated by Zoe Cardon.

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Weintraub, M.N., Scott-Denton, L.E., Schmidt, S.K. et al. The effects of tree rhizodeposition on soil exoenzyme activity, dissolved organic carbon, and nutrient availability in a subalpine forest ecosystem. Oecologia 154, 327–338 (2007). https://doi.org/10.1007/s00442-007-0804-1

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  • DOI: https://doi.org/10.1007/s00442-007-0804-1

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