The effect of microbial communities on soil hydrological processes: A microcosm study utilising simulated rainfall

The effects of soil microbial communities upon hydrological processes in relation to water holding capacity, run-off and percolation were assessed using sterile and non-sterile microcosms subjected to simulated rainfall. The treatments comprised a non-sterile field soil, soil sterilised by gamma-irradiation and sterile soil re-inoculated with field soil. Microbial biomass C was determined by chloroform fumigation–extraction and community structure by phospholipid fatty acid (PLFA) analysis. These properties were measured at the top, middle and bottom regions of the sloped (12°) microcosms. The field soil treatment had a significantly greater water holding capacity than the sterilised treatments. There was no significant difference in mean volumes of run-off or percolate between the treatments, although our results suggest a trend to a lower probability of run-off losses from a soil with higher microbial biomass and a greater potential for percolation of water. In re-inoculated treatments, microbial biomass was greater at the bottom of the slopes after rainfall, suggesting that the nascent community was relatively mobile. This effect did not occur in the field soil, although the community profiles in the re-inoculated and field soils were significantly different between the tops and bottoms of slope after rainfall. The soil microbial communities observed before and after rainfall application were significantly different for all treatments. The microbial community profiles associated with the run-off and percolate were significantly different to those found in the soil and also those found in the rainwater prior to application. Run-off and percolate community profiles were similar to one another, suggesting a consistency in the phenotypic structure of the phase of the microbial communities that was “water mobile”. This may be of significance when considering how microbial populations and communities disperse, and in relation to microbial quality of surface and groundwaters.