Effects of temperature and root additions on soil carbon and nitrogen mineralization in a predominantly permafrost peatland

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Approximately one-third of northern peatlands are within permafrost regions. Soil organic matter (SOM) and plant root biomass in permafrost peatlands are vulnerable to future global warming. However, previous studies have primarily focused on the response of SOM mineralization to increases in temperature without analysing the potential interaction effects of increased plant root biomass. This study investigated the influence of temperature and root additions on soil carbon and nitrogen mineralization as well as the mechanisms driving mineralization in a high latitude permafrost peatland in the Da Xing'an Mountains, Northeast China. We investigated changes in shallow soil (0–15 cm) and deep soil (15–30 cm) carbon mineralization, available N contents, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and enzyme activities in response to increasing temperature and Eriophorum vaginatum root additions by using an incubation experiment. Our results indicate that elevated temperature significantly increased soil carbon mineralization. The Q10 values of the carbon mineralization rates in the shallow soil and deep soil were 3.95 and 2.91, respectively. In contrast, the soil MBC and DOC decreased significantly, confirming that labile carbon is the main driving force of microbial mineralization activities under warming conditions. Elevated temperature significantly increased the shallow soil net N mineralization rates and increased the net nitrification rates in both soil layers. At high temperatures, ammonification rates increased in the shallow soil but decreased in the deep soil. The increase in the incubation temperature resulted in significantly increased shallow soil β-glucosidase activity and decreased invertase activity. This suggests the increased production of complex substrate enzymes, and decreased production of simple substrate-acquiring enzymes. The root additions significantly increased the soil C mineralization and stimulated the secretion of invertase by soil microorganisms. These findings indicate that future climate warming in the northern high latitude will significantly stimulate soil carbon and nitrogen mineralization in permafrost peatlands. Furthermore, increases in plant roots will enhance C accumulation and may even enhance the response of soil C mineralization to temperature, significantly impact the soil C balance in high latitude permafrost peatlands.