Effects of soil-surface microbial community phenotype upon physical and hydrological properties of an arable soil: a microcosm study

Abstract

The nature of the first few millimetres of the soil surface strongly affects water infiltration rates, generation of run-off, soil detachment and sediment transport. We hypothesized that the phenotypic community structure of the soil-surface microbiota affects the physical and hydrological properties of an arable soil. A range of contrasting microbial community phenotypes were established in microcosms by manipulating the wavelength of light reaching the soil surface, with the microcosms being incubated in the field for approximately 6 months. Phenotypes were characterized by phospholipid fatty acid (PLFA), ergosterol and chlorophyll analysis. The microcosms were then subjected to simulated rainfall at an intensity of 60 mm hour−1 for 20 minutes at a slope gradient of 9°. Water infiltration rates, run-off generation, soil loss (including a particle-size analysis of the sediment) and soil-surface shear strength were quantified. Distinct microbial phenotypes developed on the soil surfaces with UV-A and restricted-UV treatments when compared with subsurface layers. There was significantly greater fungal biomass in the no-light treatment when compared with all other treatments, with approximately 4.5 times more ergosterol being extracted from the subsurface layer of the no-light treatment when compared with other treatments. The no-light treatment produced the greatest amount of run-off, which was approximately 15% greater than the restricted photosynthetically-active radiation (PAR) treatment. Significant differences between treatments were also found in shear strengths, with increasing strength being correlated with increasing ergosterol concentration. Water infiltration, erosion and the sediment concentrations in run-off were not significantly different between treatments. This work demonstrates that the quality of light reaching the soil surface affects the microbial phenotype, in turn producing functional consequences with regard to the physical and hydrological properties of arable soil surfaces.