Soil respiration and extracellular enzyme production respond differently across seasons to elevated temperatures

Background and aims The activity of extracellular enzymes is one control on soil organic matter decomposition and serves as a driver of heterotrophic soil respiration. To understand how temperature sensitive enzyme reactions will influence the processing of soil carbon substrates at elevated temperatures, we deployed a passive warming experiment in a deciduous forest with highly invaded understory plant communities and high soil nitrogen concentrations. Methods We seasonally assessed six extracellular enzyme activities and measured soil respiration in the field and in laboratory incubations, to determine if soil carbon use and nutrient cycling responded to 3.5 years of warming. Results Field measurements indicate soil respiration was 24% lower and the production of the recalcitrant C-acquiring enzyme phenoloxidase was also lower in warmed plots during fall and winter. In the spring, phosphate (P) acquiring enzyme activity increased in response to warming. In lab incubations, soil respiration was not different between warmed and control soils. Conclusions Despite minimal changes to C stores after 3.5 years of warming, recalcitrant C- use and nutrient processing enzymes responded differentially to higher temperatures in fall, winter, and spring. This suggests that C- and nutrient cycle responses to warming can change throughout the seasons, perhaps mediated by plant phenological changes.