Soil microbial communities are extremely diverse, and bacteria and fungi both play integral roles in soil function and health. However, the factors that influence the spatial and temporal distribution of microbial communities are poorly understood, partly due to heterogeneity of environmental factors across a landscape. This study aims to: (1) understand how environmental factors influence microbial community structure and spatial and temporal distribution on a regional landscape scale, and (2) link microbial community structure to soil health. To capture the heterogeneity present in the landscape, soil samples were collected during late spring and early summer across the state of Oregon, stratified by Common Resource Area. A subset of those sites was then resampled monthly over one year to examine the temporal dynamics of microbial communities. A suite of physical and chemical properties were measured for each soil sample. Accompanying all soil samples was an onsite evaluation of soil and land use condition. To determine microbial phylogenetic diversity, DNA was extracted and 16S rRNA gene (bacteria) and ribosomal ITS region (fungi) were sequenced using the Illumina MiSeq platform. A custom bioinformatics pipeline was used to process sequencing reads into an OTU table. The relationship between community composition and environmental influences was examined using ordination techniques and network analysis.
Large amounts of variation in physical and chemical properties occurred over the sampled area; for example, pH ranged from 3.5 to 9.5. Even with the high variability in soil microbial community structure, a significant amount of variation was explained by soil taxonomy and land use (PERMANOVA R2 of 0.25 and 0.22 respectively, p value of 0.001). Although further research is needed to parse out the fine-scale controls on community composition, broad relationships between soil community structure and environmental factors were observed and will benefit our ability to manage ecosystem processes across a regional landscape.