Effect of drainage on microbial enzyme activities and communities dependent on depth in peatland soil

Water tables in high-latitude peatlands are expected to fall because of climate change, with significant consequences for carbon cycling in these ecosystems. At present, the understanding of how climate-induced changes will affect soil microbial communities and functions in peatlands still remains controversial. In this study, we compared the potential activities of soil oxidase and hydrolytic enzymes and microbial communities at different depths in a minerotrophic peatland, part of which had been drained for many years and part of which was natural. The results showed that the microbial communities and enzyme activities differed considerably between the drained peat and the natural peat, and that the degree of change varied by depth in the profile. The soil oxidase activities and hydrolase activities (β-1,4-N-acetylglucosaminidase and acid phosphatase) in the oxic zone (0–10 cm) were higher in the drained peat than in the natural peat, but the β-1,4-glucosidase activities decreased in the oxic zone after drainage. Soil enzyme activities in the anoxic zone were lower in the drained peat than in the natural peat. This suggests that drainage disturbance in this peatland does not support enhanced oxidative enzyme activity as hypothesized by the “enzyme-latch” mechanism. The soil total phospholipid fatty acids (PLFAs) and bacterial, fungal, and actinomycetic PLFAs in the oxic zone were lower in the drained peat than in the natural peat. The total PLFAs and bacterial PLFAs were higher in the transitional zone of the drained peat than the natural peat, but remained similar in the anoxic zone of the drained and natural peat. The fungi/bacteria and gram-positive/gram-negative ratios were lower in the drained peat than in the natural peat. The soil bacterial communities was strongly and positively linked with the β-1,4-glucosidase activities involved in carbon transformation, whereas the fungi was positively associated with oxidase activities driving carbon oxidation. We found that these variations in the microbial communities and enzyme activities were associated with differences in the litter quality, soil organic carbon, soil moisture content, and the pH between the drained peat and natural peat. These observations indicate a modification in microbial communities and their activities reflective of changing peat C cycling. The observed reduction in microbial biomass with peatland drainage appears to have also resulted in reductions in enzyme activity suggesting potential limits to the ‘enzyme-latch’ mechanism for peatland C loss following longer-term drainage.