Soil bacterial community structure changes following disturbance of the overlying plant community

The effect of plant species identity and diversity on the spatial and temporal differentiation in bacterial community structure in the active root zone was studied at a field site that was treated with herbicide, burned, and then reseeded with native grass species. Treatments were arranged in three blocks. The blocks corresponded to an elevational gradient that was used as a surrogate for moisture differences across the field. Samples were collected before and after devegetation, and eight times thereafter, over the subsequent year. The soil samples were examined for bacterial abundance (direct counts) and bacterial community structure by the genetic fingerprinting techniques randomly amplified polymorphic DNA (RAPD) and denaturing gradient gel electrophoresis (DGGE) of whole-community DNA extracts. The bacterial abundance was relatively constant in both time and space. Discriminant function analysis and the Mantel test revealed clear temporal trends in community structure throughout the entire 2-year study that coincided with the overall development of the grasses in the field. Spatial differentiation of community structure was clear among the blocks, suggesting differences in community structure based on soil moisture content. Significant differences were also observed between control and treated plots. Spatial and temporal change in the bacterial community was evident, and bacterial and plant succession coincided temporally. Differences in the bacterial communities that developed were also affected by the soil moisture.