The spatial distribution of exoenzyme activities across the soil micro-landscape, as measured in micro- and macro-aggregates, and ecosystem processes

The spatial ecology of soil microbial communities and their functioning is an understudied aspect of soil microbial ecology. Much of our understanding of the spatial organisation of microbial communities has been obtained at scales that are inappropriate for identifying how microbial functioning and spatial patterns are related. In order to reveal the spatial strategies of soil microorganisms, we measured the microscale spatial distribution of 6 exoenzyme activities (EEA) and related them to the catalytic potential of three soils. The relationship between EEA profiles and microbial community structure was also measured in soil aggregates. All the EEA exhibited scale-invariant spatial clustering. The extent of spatial clustering varied significantly among EEA, suggesting that microbial communities employ different spatial strategies when foraging for different elements. The dispersed distribution of alkaline phosphatase suggests that microorganisms invest more heavily in the acquisition of P. The EEA associated with the C and N cycles, but not the P cycle, were significantly affected by management practices in the loamy soil. A significant negative relationship between the extent of spatial clustering of EEA and the overall intensity of the EEA was identified in the two loamy soils, indicating that the microscale spatial ecology of microbial activity may have a significant impact on biogeochemical cycles. No relationship was found between microbial community structure and EEA profiles in aggregates. However, a number of negative relationships between the relative abundance of certain taxa and the most dispersed EEA (alkaline phosphatase and β-glucosidase) were found, suggesting that these taxa make the EEA products available by means other than the production of exoenzymes (e.g. solubilisation of phosphate through the production of organic acids).