Decoupling environmental filtering and host specificity of ectomycorrhizal fungi in a Bornean lowland tropical rainforest
The role that mycorrhizal fungal associations play in the assembly of long-lived tree communities is poorly understood, especially in tropical forests, which have the highest tree diversity of any ecosystem. The lowland tropical rainforests of Southeast Asia are characterized by high levels of species richness within the family Dipterocarpaceae, the entirety of which has been shown to form obligate ectomycorrhizal (ECM) fungal associations. Differences in ECM assembly between co-occurring species of dipterocarp have been suggested, but never tested, as a mechanism for maintaining the coexistence of closely related tree species in this family. Testing this hypothesis has proven difficult because the assembly of both dipterocarps and their ECM associates co-vary with the same edaphic variables. In this study, I used a soil metagenomic approach to evaluate how ECM fungi are structured within and across a clay-sand soil nutrient ecotone in a mixed-dipterocarp rainforest in Malaysian Borneo. I then compared assembly patterns of ECM fungi in bulk soil to ECM root tips collected from three ecologically distinct species of dipterocarp. This design allowed me to decouple the relative influence of host tree and soil properties on ECM assembly, and enabled me to test whether ECM fungi are more strongly structured by soil physiochemical properties or host specificity. ECM fungal communities were identified using DNA sequencing. Like previous studies of ECM fungi on this plot, I found that edaphic variables strongly structured both the bulk soil and root tip ECM fungal communities. However, I also found significantly different ECM communities associated with two of my three dipterocarp species. These results suggest that ECM fungal assembly is shaped by a combination of biotic and abiotic factors, and that the soil edaphic niche occupied by different dipterocarp species may be mediated by distinct ECM fungal assemblages. ^
Essene, Adam Lang, "Decoupling environmental filtering and host specificity of ectomycorrhizal fungi in a Bornean lowland tropical rainforest" (2015). ETD Collection for Fordham University. AAI1601931.