The effects of insects, nutrients, and plant invasion on community structure and function above- and belowground

Authors

  • Phoebe Wright,

    1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee
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  • Melissa A. Cregger,

    1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee
    2. Institute for Genomic Biology, University of Illinois, Urbana, Illinois
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  • Lara Souza,

    1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee
    2. Oklahoma Biological Survey and Department Microbiology and Plant Biology, University of Oklahoma, Norman, Oklahoma
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  • Nathan J. Sanders,

    1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee
    2. Center for Macroecology Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
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  • Aimée T. Classen

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee
    2. Center for Macroecology Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
    • Correspondence

      Aimée T. Classen, Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, DK-2100 Copenhagen, Denmark. Tel: +45 35-32-22-22; Fax: +45 46-82-74-83; E-mail: atclassen@gmail.com

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Abstract

Soil nutrient availability, invasive plants, and insect presence can directly alter ecosystem structure and function, but less is known about how these factors may interact. In this 6-year study in an old-field ecosystem, we manipulated insect abundance (reduced and control), the propagule pressure of an invasive nitrogen-fixing plant (propagules added and control), and soil nutrient availability (nitrogen added, nitrogen reduced and control) in a fully crossed, completely randomized plot design. We found that nutrient amendment and, occasionally, insect abundance interacted with the propagule pressure of an invasive plant to alter above- and belowground structure and function at our site. Not surprisingly, nutrient amendment had a direct effect on aboveground biomass and soil nutrient mineralization. The introduction of invasive nitrogen-fixing plant propagules interacted with nutrient amendment and insect presence to alter soil bacterial abundance and the activity of the microbial community. While the larger-scale, longer-term bulk measurements such as biomass production and nutrient mineralization responded to the direct effects of our treatments, the shorter-term and dynamic microbial communities tended to respond to interactions among our treatments. Our results indicate that soil nutrients, invasive plants, and insect herbivores determine both above- and belowground responses, but whether such effects are independent versus interdependent varies with scale.

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