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Plant species richness, elevated CO2, and atmospheric nitrogen deposition alter soil microbial community composition and function

Authors

  • HAEGEUN CHUNG,

    1. School of Natural Resources & Environment, 440 Church Street, University of Michigan, Ann Arbor, MI 48109, USA,
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  • DONALD R. ZAK,

    1. School of Natural Resources & Environment, 440 Church Street, University of Michigan, Ann Arbor, MI 48109, USA,
    2. Department of Ecology and Evolutionary Biology, 830 North University Avenue, University of Michigan, Ann Arbor, MI 48109, USA,
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  • PETER B. REICH,

    1. Department of Forest Resources, 1530 Cleveland Avenue, University of Minnesota, St Paul, MN 55108, USA
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  • DAVID S. ELLSWORTH

    1. School of Natural Resources & Environment, 440 Church Street, University of Michigan, Ann Arbor, MI 48109, USA,
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Present address: Haegeun Chung, Department of Plant Sciences, One Shields Avenue, University of California, Davis, CA 95616, USA. tel. +1 530 752 3450, fax +1 530 752 4361, e-mail: hgchung@ucdavis.edu

Abstract

We determined soil microbial community composition and function in a field experiment in which plant communities of increasing species richness were exposed to factorial elevated CO2 and nitrogen (N) deposition treatments. Because elevated CO2 and N deposition increased plant productivity to a greater extent in more diverse plant assemblages, it is plausible that heterotrophic microbial communities would experience greater substrate availability, potentially increasing microbial activity, and accelerating soil carbon (C) and N cycling. We, therefore, hypothesized that the response of microbial communities to elevated CO2 and N deposition is contingent on the species richness of plant communities. Microbial community composition was determined by phospholipid fatty acid analysis, and function was measured using the activity of key extracellular enzymes involved in litter decomposition. Higher plant species richness, as a main effect, fostered greater microbial biomass, cellulolytic and chitinolytic capacity, as well as the abundance of saprophytic and arbuscular mycorrhizal (AM) fungi. Moreover, the effect of plant species richness on microbial communities was significantly modified by elevated CO2 and N deposition. For instance, microbial biomass and fungal abundance increased with greater species richness, but only under combinations of elevated CO2 and ambient N, or ambient CO2 and N deposition. Cellobiohydrolase activity increased with higher plant species richness, and this trend was amplified by elevated CO2. In most cases, the effect of plant species richness remained significant even after accounting for the influence of plant biomass. Taken together, our results demonstrate that plant species richness can directly regulate microbial activity and community composition, and that plant species richness is a significant determinant of microbial response to elevated CO2 and N deposition. The strong positive effect of plant species richness on cellulolytic capacity and microbial biomass indicate that the rates of soil C cycling may decline with decreasing plant species richness.

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