Recent Advancements in Understanding the Ecology of Soil Extracellular Enzymes.

Extracellular enzymes are the agents of detritus decomposition, and are critical for biogeochemical cycling in soils.  Despite decades of research, we have only a rudimentary understanding of the controls on enzyme production, stabilization, turnover, and in-situ activity.  This limits our ability to interpret measured enzyme activities in an ecological framework.  We will present several recent innovations that are advancing our understanding of how soil microbial community interactions with their abiotic environment affect in-situ enzyme activity.  In Arctic tundra soils, we developed a model for in-situ Β-glucosidase activity by extrapolating from enzyme activities measured in the lab at a range of temperatures to actual field temperatures.   The results of this model suggest that enzyme activity is limited by temperature in the winter and by nitrogen limitation to enzyme production in the summer.   In a climate warming and precipitation manipulation experiment in a Boston old field, we found increased enzyme activities in drought plots despite a decrease in microbial biomass.  Evidence from the temperature sensitivity of enzyme activity suggests that drought decreased the degradation rate of enzymes, resulting in larger enzyme pools.  We will also discuss the importance of tannin inhibition of enzymes, which an often overlooked control on in-situ enzyme activities.  We have found that different  enzymes are not equivalently affected by increasing tannin concentrations, suggesting that changes in plant litter tannin chemistry in response to climate change could alter soil nutrient stoichiometry.  By focusing on controls on in-situ enzyme activity, we hope to advance our understanding of the ecology of soil extracellular enzymes.