Tuesday, August 7, 2007

PS 23-19: The effects of suppressed mycorrhizal fungi and increased nitrogen on above- and belowground competition intensity in two native plant species during grassland restoration

Michael Fell, University of Wisconsin -- Eau Claire, Tali D. Lee, University of Minnesota - Duluth, Stephen Bentivenga, University of Wisconsin - Oshkosh, and Evan Weiher, University of Wisconsin-Eau Claire.

Competition is an important process in natural environments and it can greatly impact organism success. The goal of this experiment was to assess the effects of both above and below-ground competition on plant performance, and is part of a larger experiment assessing the effects of fertilizer and fungicide on community assembly during prairie restoration. The experiment was done using a factorial design of added fungicide (18 mg chlorothalonil m-2 yr-1) and fertilizer (15 g N m-2yr-1 as ammonium nitrate). Within each of 15 plots, we had three competition treatments (no competition, below-ground competition, and full competition) in which two phytometers were grown (Andropogon gerardii and Heliopsis helianthoides). In both A. gerardii and H. helianthoides the below-ground relative interaction intensity (RII) was significantly increased with the addition of fungicide by about 4-fold and 2-fold respectively while no change was seen in above-ground RII. Total RII also showed an increase in both species when fungicide was added, however the relationship was only marginally significant in A. gerardii. Both species had highly similar levels of mycorrhizal fungal colonization in both control (24.6%) and fungicided plots (16%) Added nitrogen did not significantly affect competition intensity.