Effects of vegetation type and soil horizon on soil bacterial and fungal communities in a dry–hot valley

Soil horizon and vegetation cover significantly impact the spatial patterns of soil fungal and bacterial communities. However, such impacts and their interactions are poorly characterized in dry–hot environments. Soil samples were collected from two soil horizons (humus and mineral) along a vegetation gradient (shrubland, grassland, and shrub–grass ecotone) in a dry-hot valley of Southwestern China to assess the effects of vegetation versus soil horizons on shaping soil microbial communities. We used denaturing gradient gel electrophoresis to estimate the microbial spatial pattern change across the vegetation gradients and clone libraries targeting small subunit rRNA genes to characterize the microbial community structures between distinct vegetation types and soil horizons. Bacterial DNA profile patterns were not significantly different across vegetation types but strongly correlated with soil horizons, with significant interaction effects. By contrast, fungi were remarkably different across vegetation types and soil horizons, without significant interactions effect. Distinct vegetation types did not necessarily harbor distinct bacterial or fungal community compositions. Rather, both community compositions were most strongly affected by the soil horizons. Together with these results, the soil vertical heterogeneity rather than vegetation changes is suggested to best predict shifts in soil microbial communities in this dry-hot valley area.