科研之友
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摘要
Climate warming is resulting in increases in the frequency and intensity of summer droughts in the Great Lakes-St. Lawrence forest region (Ontario, Canada), raising concerns for the fate of C stores. We hypothesized that deeper peat historically existing beneath the water table would produce significant CO2 efflux during summer droughts. To test this hypothesis, we collected saturated peat cores, partitioned them into depth intervals, incubated the peat under conditions that resulted in peat drying, and monitored daily CO2 production together with potential drivers of CO2 production, including peat quality, microbial biomass, and microbial extracellular enzyme activity. Peat CO2 production (mu mol CO2 min(-1) g(-1) dry soil) was highest in the top 30 cm of the peat profile, with the highest production at intermediate volumetric water content (VWC). Peat substrates fuelling CO2 production had quotients of C to N of <20 and were characterized by more labile forms of C. Microbial biomass C (mg C g(-1) dry soil) and most microbial extracellular enzymes (nmol g(-1) h(-1)) were also highest in the top 30 cm of the peat profile. Activities of microbial extracellular enzymes shifted in their contribution to CO2 production as the peat dried, with hydrolases positively related to CO2 under dry conditions (5-35%) and negatively under wet conditions (65 and 85%), with phenol oxidase showing the opposite pattern. Currently, the relatively poor quality (i.e., high C/N) of peat in catotelm limits rapid release of CO2 with water table declines. However, this substantial C store may be vulnerable to decomposition if constraints on quality are alleviated.
- 出版日期2014-6
