PARENT SESSION
Poster Session 38: Mutualism / Parasitism
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Dynamics and competitive interactions: The role of ectomycorrhizal associations in tropical monodominance: Can ectomycorrhizal fungi suppress saprotrophic fungi?
McGuire, Krista1, Zak, Donald1, 1 University of Michigan, Ann Arbor, MI, USA
ABSTRACT- Tree diversity patterns within and across tropical rain forests are not uniform, and the contribution of mycorrhizal associations in generating and maintaining these patterns is not known. While most tropical trees form arbuscular mycorrhizal (AM) associations, there is a high correlation between monodominance, where one tree species comprised >80% of the canopy, and ectomycorrhizal associations. Several mechanisms for tropical ECM dominance have been suggested and one hypothesis that has been often cited is that ECM fungi can suppress saprotrophic microorganisms and circumvent limiting nutrients back to the associate tree. This is based on the well-supported supposition that ECM fungi, unlike AM fungi have the enzymatic capabilities to access organically bound nutrients. However, despite these capabilities, ECM fungi are poorer competitors for organically bound nutrients than saprotrophs, and there is evidence that suppression of saprotrophic competitors may occur to compensate for ECM fungi's poorer saprotrophic abilities. To test this hypothesis, we investigated the relative abundance of saprotrophic fungi in an ECM monodominant forest and a neighboring, high-diversity rain forest containing predominantly AM trees in central Guyana. We used phospholipid fatty acid (PLFA) analysis to determine total microbial biomass and relative representation of microbial groups between monodominant and mixed forests, and to assess compositional differences in the fungal communities between the forest types we extracted and amplified fungal rDNA directly from frozen soil cores. Using general fungal primers, the SSU (18s small subunit) rDNA gene was selectively amplified using PCR. The resulting DNA fragments were separated using denaturing gradient gel electrophoresis (DGGE) and the resulting bands were re-amplified, sequenced and identified using the BLAST database. Results indicate that the dominant fungal groups in the high-diversity forest are saprotrophic and that there are more species of saprotrophic fungi in this forest type than in the ECM dominated forest. This suggests that ECM fungi may be suppressing saprotrophic fungi in the monodominant forest, and may be one mechanism by which ECM trees become locally dominant in tropical rain forests.
Key words: mycorrhizal associations, tropical rain forest diversity, monodominance, seedling competition