Spatial Patterns of Soil Microbial Communities on a Regional Scale.

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 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 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 suite of physical and chemical properties were measured for each soil sample. 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. Accompanying all soil samples was an onsite evaluation of soil and land use condition. Community composition was examined using nonmetric non-dimensional scaling (NMDS) and correlations were established between soil factors and community structure using Mantel tests.

Large amounts of variation in physical and chemical properties occurred over the sampled area; for example, pH ranged from 3.5 to 9.5.  CO₂ evolution was significantly dependent on current land use up to a two-fold difference observed between the means (rangeland=cropland<forested=pasture).

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.