Soil bacterial diversity based on management and topography in a silvopastoral system

Soil microorganisms play crucial roles in nutrient cycling and provisioning ecosystem services. However, little is known about how soil microbial communities are affected by soil management and landscape position in silvopastures. The current study aimed to understand effects of forage species [non-native, cool season orchardgrass (Dactylis glomerata L.) and a warm-season native grass mix (Andropogon gerardii L. and Schizachyrium scoparium L.) planted in strips between hedgerows], soil fertility (poultry litter and a control), and soil moisture regimes (aquic and udic) on soil bacterial communities to evaluate linkages between terrain attributes and soil bacterial assemblages. Thirteen terrain attributes representing topographic variability were clustered into four topographic functional units (TFUs) using the k-means method, and their impact on soil microbial diversity was evaluated. Illumina sequencing results identified a soil moisture regime × forage species interaction, with native grass species under wet (aquic) conditions resulting in the most diverse microbial assemblages relative to dry (udic) and wet soil conditions for the non-native forage (orchardgrass). These results suggest an enhanced soil microbial diversity under native grasses with greater available soil water. Overall, microbial diversity was negatively correlated with elevation, suggesting niche differentiation and microbial preference for lower elevations. Overall, TFUs and selected terrain attributes may be useful for predicting microbiota dynamics in integrated tree-livestock systems.