The Effects of Freeze-Thaw Cycles on Methane Emissions From Peat Soils of a High-Altitude Peatland

The Qinghai- Tibet Plateau (QTP), which embodies the largest area of permafrost at mid-low altitudes of the world, has been experiencing rapid permafrost degradation and changes in freeze-thaw processes for the past decades. However, the responses and potential feedbacks of the methane flux from peatlands on the QTP to changing freeze-thaw cycles (FTCs) remain unknown. In this study, we collected peat soils from the Zoige peatlands, the largest peatland complex on the QTP, to examine methane emissions under simulated diurnal FTC scenarios. In incubation experiments of 15 days, two freeze-thaw temperature ranges of -5 to 4 degrees C (mild) and -15 to 4 degrees C (intense) were applied to two sets of peat soil samples, and each of them was characterized by 100% or 80% maximum water holding capacity (MWHC). The results showed that the peak of methane emission from the peat soil occurred after the first freeze-thaw cycle (FTC1), with the highest reaching a value of 0.103 mg kg soil(-1)center dot h(-1). Generally, the cumulative methane emissions were elevated by FTCs, and relative higher rates of methane emissions were found for the 2nd FTC to the 15th FTC, compared with those from low-altitude peatlands. Methane emissions were significantly correlated to the export of dissolved organic carbon (DOC) and the activities of beta-D-cellobiosidase and phenol oxidase in various freeze-thaw conditions. This study highlights the importance of FTCs in stimulating methane emissions and implies that methane emissions during FTCs from high-altitude peatlands would increase under a warmer climate in the future.