Uncoupling environmental filtering and host specifiicty of ectomycorrhizal fungi in a Bornean lowland tropical rainforest

Background/Question/Methods

Mycorrhizal fungi provide the physiological link between soil nutrients and 80% of all terrestrial plant species.  Although both plant and mycorrhizal fungal community structure tend to differentiate along gradients of soil nutrient content, it is unclear to what extent these community changes reflect host specificity or environmental filtering.  In this study, we attempt to uncouple the influence of biotic and abiotic factors on ectomycorrhizal community structure across a soil ecotone in a Bornean rainforest.  Using Illumina high-throughput sequencing of bulk soil samples and Sanger sequencing of ectomycorrhizal root tips collected from three species of Shorea (Dipterocarpaceae), we tested the following hypotheses: 1) variation in ectomycorrhizal fungal community structure reflects soil nutrient partitioning by soil type and soil horizon, and 2) ectomycorrhizal fungal community structure varies within soil type between host species of Shorea.

Results/Conclusions

1) In both our bulk soil and ectomycorrhizal root tip samples, we found significantly different ectomycorrhizal community structure on each soil type.  Additionally, we found significant differences between the ectomycorrhizal compositions of different soil horizons, even within the same soil core.  This vertical structuring indicates that different fungal taxa utilize different nutrient resources in the soil.  2) We found no evidence that host species of Shorea influenced ectomycorrhizal community structure on either soil type.  This result suggests that while both ectomycorrhizal fungi and their plant hosts respond to the abiotic environment, they assemble independently of each other.