Hugh A.L. Henry
Department of Biology, University of Western Ontario, London, Ontario N6A 5B7, Canada.
Assays for extracellular enzyme activity (EEA) have become a common tool for studying soil microbial responses in climate change experiments. Nevertheless, measures of potential EEA, which are conducted under controlled conditions, often do not account for the direct effects of climate change on EEA that occur as a result of the temperature and moisture dependence of enzyme activity in situ. Likewise, the indirect effects of climate on EEA in the field, that occur via effects on microbial enzyme producers, must be assessed in the context of potential changes in plant and soil faunal communities. Here, EEA responses to warming and altered precipitation in field studies are reviewed, with the goal of evaluating the role of EEA in enhancing our understanding of soil and ecosystem responses to climate change. Seasonal and interannual variation in EEA responses to climate change treatments are examined, and potential interactions with elevated atmospheric CO2, increased atmospheric N deposition and changes in disturbance regimes are also explored. It is demonstrated that in general, soil moisture manipulations in field studies have had a much greater influence on potential EEA than warming treatments. However, these results may simply reflect the low magnitude of soil warming achieved in many field experiments. In addition, changes in plant species composition over the longer term in response to warming could strongly affect EEA. Future challenges involve extending studies of potential EEA to address EEA responses to climate change in situ, and gaining further insights into the mechanisms, such as enzyme production, stabilization and turnover, that underlie EEA responses.