Heterogeneous landscape promotes distinct microbial communities in an imperiled scrub ecosystem

Habitat heterogeneity is a key driver of biodiversity of macroorganisms, yet how heterogeneity structures belowground microbial communities is not well understood. Importantly, belowground microbial communities may respond to any number of abiotic, biotic, and spatial drivers found in heterogeneous environments. Here, we examine potential drivers of prokaryotic and fungal communities in soils across the heterogenous landscape of the imperiled Florida scrub, a pyrogenic ecosystem where slight differences in elevation lead to large changes in water and nutrient availability and vegetation composition. We employ a comprehensive, large-scale sampling design to characterize the communities of prokaryotes and fungi associated with three habitat types and two soil depths (crust and subterranean) to evaluate (i) differences in microbial communities across these heterogeneous habitats, (ii) the relative roles of abiotic, biotic, and spatial drivers in shaping community structure, and (iii) the distribution of fungal guilds across these habitats. We sequenced soils from 40 complete replicates of habitat × soil depth combinations and sequenced the prokaryotic 16S and fungal internal transcribed spacer (ITS) regions using Illumina MiSeq. Habitat heterogeneity generated distinct communities of soil prokaryotes and fungi. Spatial distance played a role in structuring crust communities, whereas subterranean microbial communities were primarily structured by the shrub community, whose roots they presumably interacted with. This result helps to explain the unexpected transition we observed between arbuscular mycorrhiza-dominated soils at low-elevation habitats to ectomycorrhiza-dominated soils at high-elevation habitats. Our results challenge previous notions of environmental determinism of microbial communities and generate new hypotheses regarding symbiotic relationships across heterogeneous environments.