While current understandings of intercontinental microbial biogeography have been elucidated by advancements in sequencing technologies, the role of biotic and abiotic factors in shaping soil communities at smaller spatial scales remains unclear. At the global scale, fungal and bacterial communities are structured by a number of different factors; for example, across wide latitudinal ranges, pH explains much of the intercontinental biogeography of soil bacteria, and soil moisture is a primary driver of fungal distributions. Although many biomes are restricted in their latitudinal ranges, both aboveground plant communities, and the soil environments microbial communities occupy, exhibit great heterogeneity both at scales ranging from local (kilometer) to regional (hundreds of kilometers).
Here we assess whether ecosystem type, climate, and edaphic factors structure microbial communities at a regional scale. Across the state of Minnesota, we characterized soil microbial communities from common ecosystem types including prairies, deciduous forests, coniferous forests, oak savannas, and wetlands. We hypothesized that both fungal and bacterial community composition would vary between ecosystem types, while fungi and bacteria might respond differently to climate or edaphic characteristics. From the same soil cores, DNA was extracted for fungal and bacterial sequencing on the Illumina MiSeq platform, targeting the ITS1and 16S regions, respectively.
Fungal and bacterial communities were structured by a combination of biotic and abiotic factors at the regional scale. Ecosystem type was responsible for explaining 14.4% and 20.1% of fungal and bacterial community composition, respectively (p < 0.001, p < 0.001). Regarding the microbial relationship to aboveground communities, the composition of the plants at a given site explained 68.9% of fungal community composition and 35.9% of bacterial community composition (pfung < 0.001, pbac < 0.001). In constrained analyses including suites of climatic and edaphic characteristics, ecosystem type and pH were the best predictors of fungal community composition (r2 = 0.19, ptype < 0.001, ppH < 0.001). One third of the variation in bacterial community composition could be attributed to ecosystem type, pH, and winter precipitation (r2 = 0.324, ptype < 0.001, ppH < 0.001, pprcp = 0.007). Our study suggests that across different ecosystems in a single region, similar biotic and abiotic factors structure both fungal and bacterial communities. In addition to the commonly acknowledged importance of pH for microbial taxa, aboveground plant communities, which are highly variable among ecosystems, are also an important driver of belowground community dynamics at the ecosystem scale.