INTRODUCTION Wetlands are transitional zones between ter- restrial and aquatic ecosystems, having many distinguishing features (Mitsch and Gosselink, 1993). The biogeochemistry of wetlands is highly unique compared to upland ecosystems or aquat- ic sediments, because diverse redox potential regimes co-exist in a close proximity. In particu- lar, two important aspects of wetland biogeo- chemistry have been extensively studied. First, wetlands are one of the main sources of methane (CH 4 ) and nitrous oxide (N 2 O), which are much stronger greenhouse gas than carbon dioxide on a molar basis (Rodhe, 1990). The other impor- tance of wetlands is the production and decom- position of dissolved organic carbon (DOC), which is dominant form of organic carbon in many aquatic ecosystems. DOC is an important compo- nent of organic energy pathways in ecosystems (Middelboe and Sondergaard, 1993), and hence the amount and the composition of DOC affect substrate availability for heterotrophic bacterial growth (Mann and Wetzel, 1995). Further, sever- al studies have shown that DOC in wetlands would affect various microbial-mediated process- es such as trace gas flux (Bianchi et al., 1996) and extracellular enzyme activities (Freeman et al., 1998). In the decomposition and nutrient cycling in aquatic or terrestrial ecosystems, extracellular hydrolysis by enzymes has been reported as a critical step for the following reasons. First, other Korean J. Limnol. 39 (4):435~444 (2006) ─ 435 ─ * Corresponding Author: Tel: +82-2-3277-3916, Fax: +82-2-3277-3275, E-mail: hjkang@ewha.ac.kr Importance of Extracellular Enzyme Activities in Northern Peatland Biogeochemistry-Possible Coupling with Trace Gas Emission and DOC Dynamics Kang, Hojeong*, Chris Freeman 1 and Seok-Soon Park (Department of Environmental Science and Engineering, Ewha Womans University, Seoul, Korea 1 School of Biological Sciences, University of Wales, Bangor, LL57 2UW, UK) A suite of extracellular enzyme activities involved in organic carbon decomposition were determined in three northern peatlands (a bog, a fen, and a swamp) over a 12 month period along with trace gas (CO2 and N2O) flux and DOC dynamics in the wetlands. The activities varied 0.008-0.066 μmole g -1 min -1 , 0.003-0.021 μmole g -1 min -1 , 0.003-0.016 μmole g -1 min -1 , 0.004-0.047 μmole g -1 min -1 , for β-glucosidase, cellobio- hydrolase, β-xylosidase, and N-acetylglucosaminidase, respectively. In general, the activities were highest in the forested swamp followed by the fen and the bog. When the data from three wetlands are combined, the enzyme activities exhibited significant positive correlations with trace gas emission and available carbon. Further, the average activity of 4 enzymes explained about 20-40% of the variations of trace gas emssion and available carbon. The results indicate that enzymes related to the mineralization of organic carbon may play an important role in trace gas f lux and DOC dynamics in northern peatlands. Key words : cellulose, organic carbon, peat, soil enzyme, wetland