Competitive interactions among three ectomycorrhizal fungi and their relation to host plant performance

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2007.01306.x Byline: PETER G KENNEDY (*[dagger][paragraph]), SARA HORTAL ([double dagger]), SARAH E BERGEMANN (s.), THOMAS D BRUNS ([dagger]) Keywords: ectomycorrhizas; fungi; interspecific competition; Pinus muricata; real-time PCR; Rhizopogon; symbiosis Abstract: Summary Competition strongly influences many species assemblages, but its role in mycorrhizal fungal interactions is not well understood. We examined interactions among three ectomycorrhizal (ECM) species to determine if the structure of competition could be characterized by either competitive networks (where no clear hierarchy exists in the outcome of competition between various species pairs) or competitive hierarchies (where one species out competes all other species). Using a bioassay experiment, we inoculated Pinus muricata seedlings with three Rhizopogon species (R. occidentalis, R. salebrosus, and R. vulgaris) in single-, two-, and three-species treatments. After 7 months, we assessed the relative abundance of each species in each treatment using real-time PCR of internal transcribed spacer rDNA. We found that R. occidentalis was strongly inhibited by R. vulgaris and R. salebrosus in all competition treatments. In contrast, R. vulgaris and R. salebrosus had similar ECM biomasses in the two-species treatment, but R. vulgaris had significantly higher biomass than R. salebrosus in the three-species treatment. In the single-species treatments, seedlings colonized by the competitive dominants had higher shoot biomass and total leaf nitrogen, but also higher percentage ECM biomass. In the multi-species treatments, seedlings had either equivalent or somewhat lower shoot biomass and total leaf nitrogen than their respective single-species treatments. Synthesis. Our results indicate that ECM competition does not appear to be characterized by strict networks or hierarchies. Instead, the outcome is dependent on the conditions of the local environment in which it occurs. There also does not seem to be a clear relationship between ECM competitive ability and plant performance, but competition does appear to negatively affect the ability of ECM fungi to provide benefits to their hosts. Author Affiliation: ([dagger])Department of Plant and Microbial Biology, 321 Koshland Hall, University of California, Berkeley, CA, USA ([double dagger]), IRTA, Departament de Proteccio Vegetal, Ctra Cabrils km 2, 08348 Cabrils, Spain, (s.)Department of Environmental Science and Policy Management, 137 Mulford Hall, University of California, Berkeley, CA, USA, and ([paragraph])Department of Biology, Lewis and Clark College, Portland, OR 97219, USA Article History: Received 31 May 2007; accepted 20 August 2007 Handling editor: Marcel van der Heijden Article note: (*) Author to whom correspondence should be addressed: Peter Kennedy, 0615 Palatine Hill Road., Lewis and Clark College, Portland, OR 97219, USA. Fax: +1 503 768 7658. E-mail: pkennedy@lclark.edu.