Change of soil labile organic carbon fractions and enzyme activities during peatland restoration in Changbai Mountains, Northeast China.

Peatlands are one of the most important terrestrial carbon storage reservoirs. The response of soil labile organic carbon fractions to environmental changes is a pivotal indicator for assessing the stability of soil organic carbon pools. Soil enzymes act as primary participants in the biogeochemical processes of peatlands, significantly influence the material cycling and energy flow. Taking natural peatlands, degraded peatlands, and peatlands restored for 3, 5, and 8 years in the Changbai Mountains as test objects, we examined the changes of soil labile organic carbon fractions, enzyme activities, soil physicochemical properties, and aboveground biomass during peatland restoration. The results showed that the contents of easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC) increased following peatland restoration. Both MBC and DOC exhi-bited a progressive increase with restoration duration, showing cumulative rises of 139.7% and 160.2%, respec-tively, after 8 years of restoration. In contrast, EOC recovered to the level comparable to natural peatland within just 3 years of restoration, exhibiting a notably rapid recovery. Restoration significantly increase the activities of β-1,4-N-acetylglucosamine glycosidase (NAG) and acid phosphatase (ACP) in the 0-10 cm soil layer. After 8 years of restoration, the activities of NAG and ACP increased by 30.1% and 84.1%, respectively. However, the activity of β-1,4-glucosidase (βG) increased by 60.8% after 3 years of restoration, decreased slightly after 5 years of restoration, and showed no significant difference between the peatland restored for 8 years and the degraded peatlands. Correlation analysis and structural equation modeling showed that soil organic carbon directly influenced soil labile organic carbon fractions, while soil labile organic carbon fractions and aboveground biomass collectively influenced soil enzyme activity. In conclusion, natural-based restoration could effectively increase soil labile organic carbon fractions and soil microbial enzyme activities, thereby promoting peatland recovery. This study would provide basic data and a reference framework for the ecological restoration and management of degraded peatlands.