Abstract:

Freezing-thawing process is an important factor controlling carbon dynamics in mid-high latitude regions. Recently, there has been a growing interest in the effects of freezing-thawing cycle (FTC) on soil carbon stability and associated bio-geochemical process in mid-high latitude regions under global warming. The effects of FTC on soil organic carbon mineralization in peatland of permafrost region are still unclear. In this study, we collected soil samples from active layer (0-15 cm and 15-30 cm) of an undisturbed permafrost peatland in the Great Hinggan Mountains, Northeast China, and then subjected them to FTC simulation and mineralization incubation experiments. Our goal was to characterize soil mineralization in peatland by FTC and to determine the corresponding influencing factors. The results showed that cumulative organic carbon mineralization including CO₂ and CH₄ ranged from 483 mg/kg to 2836 mg/kg. FTC significantly decreased peatland soil organic carbon mineralization in 0-15 cm and 15-30 cm layers, especially for the 15-30 cm soil layer that the decrease magnitude reached up to 76%. Notably, FTC obviously promoted CH₄ emission, and the emission in 15-30 cm soil layer increased by up to 145%. Meanwhile, FTC significantly increased soil dissolved organic carbon (DOC) concentration, but reduced microbial biomass carbon (MBC) concentration and amylase, cellulase and sucrase activities. Lower enzyme activities and relatively inferior quality carbon were the reasons for the decreased soil organic mineralization in FTC treatment. Under global warming, compared with the effect of only temperature increase, FTC can decrease the soil organic carbon mineralization during the short incubation stage in the permafrost peatland of Great Hinggan Mountains.

Key words: Freezing-thawing cycle, Peatland, Organic carbon mineralization, Soil enzyme, Active carbon