Dispersal, colonization, and ecological interactions of mycorrhizal fungi
Fungi play an important role in plant communities and ecosystem function. As the primary mutualists and pathogens of plants, variation in fungal community composition may have important consequences for plant fitness. One potential driver of variability in fungal community composition is dispersal. However, there is relatively little empirical data on fungal dispersal, how dispersal affects fungal communities, and how this in turn affects the ecological processes they mediate. To answer these questions we established spore sampling stations across a large area of landscape in coastal California. These sampling stations varied in their proximity to each other and contrasting vegetation types. We measured dispersal of spores at multiple time points across this landscape using qPCR and 454 pyrosequencing. We also measured colonization of ectomycorrhizal fungi at each station using sterile bait seedlings.
There is a high degree of spatial and temporal variability in the composition of fungal spores across the landscape. A large fraction of this variability appears to be stochastic as it was poorly explained by any predictor variables. This was even evident at small scales by differences in ectomycorrhizal colonization of bait seedlings within the same site. However, we also found predictable patterns in spore dispersal, as similarity of spore composition increased with spatial proximity, similarity of adjacent vegetation types, and time of year. Species of ectomycorrhizal fungi also showed consistent differences in dispersal ability, with species such as Suillus pungens producing more spores and colonizing more seedlings. This led to predictable changes in colonization by ectomycorrhizal fungi and seedling growth with distance from ectomycorrhizal host vegetation. Our results demonstrate that fungal host and habitat specificity coupled with dispersal limitation can lead to local variation in fungal community structure and plant-fungal interactions. These results suggest that understanding fungal communities their interactions with host plants also requires explicit knowledge of landscape context in addition to local environmental conditions.