title: The effects of insects, nutrients, and plant invasion on community structure and function above-and belowground.
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.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee 569 Dabney Hall, Knoxville, Tennessee, 37996.
authors.forename: Phoebe
authors.initials: P
authors.lastname: Wright
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee 569 Dabney Hall, Knoxville, Tennessee, 37996 ; Institute for Genomic Biology, University of Illinois 1206 W Gregory Rm 3405, Urbana, Illinois, 61801.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Cregger
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee 569 Dabney Hall, Knoxville, Tennessee, 37996 ; Oklahoma Biological Survey and Department Microbiology and Plant Biology, University of Oklahoma 111 E Chesapeake St., Norman, Oklahoma, 73019.
authors.forename: Lara
authors.initials: L
authors.lastname: Souza
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee 569 Dabney Hall, Knoxville, Tennessee, 37996 ; Center for Macroecology Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen Copenhagen, DK-2100, Denmark.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Sanders
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee 569 Dabney Hall, Knoxville, Tennessee, 37996 ; Center for Macroecology Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen Copenhagen, DK-2100, Denmark.
authors.forename: Aimée T
authors.initials: AT
authors.lastname: Classen
keywords: aboveground biomass; bacteria; fungi; insect; invasive plant; nitrogen-fixer; nutrient amendment; old-field ecosystem; soil enzyme activity