Does Community Composition or Environmental Variability Control Extracellular Enzyme Activity in Soil? A Spatial Analysis in a Complex Forested Landscape.

The correspondence between taxonomic composition and the suite of functional traits expressed in a community is an important issue facing all of ecology as we try to predict the outcomes of species loss and habitat change.  For soil microorganisms, extracellular enzymes represent an investment expected to increase substrate and nutrient availability.  Aggregated across the microbial community, production of extracellular enzymes has ecosystem-level consequences for soil organic matter and nutrient budgets.  In this study, we determined the extent to which taxonomic (fungal and bacterial TRFLP) and functional (extracellular enzyme activity) profiles of soil microorganisms correspond in a complex landscape, and whether they respond to similar environmental gradients.  The study took place in a forest stand in Ohio with adjacent upland, riparian, and bottomland forests.  Sampling was designed to capture spatial variability within and between these habitats, at scales ranging from 2 to 600 m.  In addition, a wide variety of soil and vegetation properties were measured.  Extracellular enzyme profiles and bacterial community composition were both found to be significantly related to several soil properties, and also displayed additional spatial autocorrelation up to 80 m.  Fungal community composition was left largely unexplained.  Enzymes and bacteria were driven similarly by soil properties, whereas different processes caused enzyme and bacterial autocorrelation.  Hence, it appears that bacterial community composition may control extracellular activity only to the extent that environmental variability controls community composition, and additional factors must also influence both independently.