Microbial responses to soil rewetting in erosional and depositional environments in relation to the organic carbon dynamics

In order to investigate the microbial responses to soil rewetting in erosional and depositional environments in relation to organic carbon dynamics, three contrastive plots (in erosional, transitional, and depositional areas) were imposed with varying erosion or deposit characteristics in a typical sloping cropland of the red soil region in south China. The cropland was rewetted uniformly by a simulated rainfall under field conditions, and the three plots in the land were sampled before and 180 h after rewetting. Soil organic carbon (SOC) pools, DNA-based microbial abundance, and community structure were measured. In response to rewetting, the erosional area had greater microbial abundance than the transitional or depositional sites. The variations in bacterial and fungal abundance were not significantly correlated with the dynamics of soil carbon pools at site or during the whole experimental period. Bacterial diversity increased immediately after rewetting at downslope positions, especially in the depositional area. Fungal community structure was less sensitive to rewetting than that of bacteria and was rather dynamic at the erosional site compared with the depositional site. Together with site variables, the carbon data set significantly (P < 0.01) explained the variations of bacterial and fungal community structures after rewetting. To conclude, site erosion or deposit characteristics may affect the drying/rewetting (D/R) susceptibility of soil biogeochemical carbon cycles by inducing shifts in functional microbial communities with different responses to rewetting.