PARENT SESSION
Oral Session #33: Biodiversity and Ecosystem Function: Nutrients, soils, microbes.
Presiding: K. Brown
Tuesday, August 6. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Species diversity and community composition of arbuscular mycorrhizal fungi in tropical forest fragments and adjacent pastures.

Aldrich-Wolfe, Laura^*,1, ¹ Cornell University, Ithaca, NY

ABSTRACT- Conversion of forest to pasture has been hypothesized to lead to declines in species richness and abundances of mycorrhizal fungi species. Evidence for such declines is currently ambiguous. In this study, I compared species diversity of arbuscular mycorrhizal (AM) fungi for three pairs of forest fragment and adjacent pasture sites in a coffee farming community in Coto Brus, southern Costa Rica. I determined species diversity of AM fungi by both direct assessment of field-collected soil samples and estimates from trap cultures in the greenhouse. Results suggest conversion of forest to pasture produces shifts in abundances of many AM fungi species rather than general declines. Species richness of AM fungi was similar in pasture and forest sites, despite the depauperate nature of the pasture plant community relative to that of forest. While some AM fungi species were common in both forest and pasture sites, others were abundant in one vegetation type and rare or absent in the other. These results suggest pasture plants support a AM fungi community that may be at least as species-rich as that of forested sites, but that differs in its composition. Inoculations of seedlings of a tropical forest tree with the divergent communities indicate that forest AM fungi provide a growth benefit to seedlings, while pasture AM fungi do not. Consequences of this shift in AM fungi species composition for forest regeneration need to be examined.

KEY WORDS: arbuscular mycorrhizal fungi, species diversity, tropics