University of Miami Coral Gable, Florida, United States
Habitat heterogeneity is a key driver of biodiversity of plants and animals. Heterogeneity, particularly for plant communities, is often generated by shifts in environmental properties (e.g., soil fertility or soil moisture) across a landscape. However, how microbial taxa in the soil respond to habitat heterogeneity is less clear. Belowground microbial communities may be responding to several environmental, biotic, and spatial drivers. Here, we explored these potential drivers of prokaryotic and fungal communities in soils in the Florida scrub, an endemic, heterogeneous ecosystem with several pyrogenic habitat types. We employed a comprehensive, large-scale sampling design to sequence the 16S (prokaryotes) and ITS (fungi) genes found in soils across three of these habitats along an elevational gradient (flatwoods, scrubby flatwoods, and rosemary scrub) at two soil depths (crust and subterranean). We used variance partitioning to determine the relative roles of soil depth, plant community, environment (e.g., elevation and time-since-fire), and spatial distance in shaping microbial community across these habitats. Finally, to extend our understanding of community function, we evaluated the distribution of fungal guilds across these habitats.
Habitat heterogeneity generated distinct communities of soil prokaryotes and fungi, as evidenced by significant community differences among the three habitat types and soil depth. Surprisingly, the surrounding plant community was a better predictor of microbial communities than the hypothesized environmental factor of elevation. Spatial distance was also an important predictor, particularly for prokaryotic communities found in the soil crusts. Furthermore, we found an unexpected transition between arbuscular mycorrhizal-dominated soil at low elevation habitat to ectomycorrhizal-dominated soils at high elevation habitat. Our results indicate that patterns of microbial communities across a heterogeneous landscape are better predicted by biotic drivers than abiotic factors, suggesting that microbial communities of the Florida scrub are responding to the existing plant community. Our findings, particularly the transition between arbuscular-dominated and ectomycorrhizal-dominated mycorrhizal systems, suggest there may be shifting symbiotic relationships across this heterogeneous landscape, and should be the focus of future work.