Methane emissions during different freezing-thawing periods from a fen on the Qinghai-Tibetan Plateau: Four years of measurements

How methane (CH4) fluxes from alpine peatlands, especially during freeze-thaw cycles, affect the global CH4 budget is poorly understood. The present research combined the eddy covariance method, incubation experiments and high-throughput sequencing to observe CH4 flux from an alpine fen during thawing-freezing periods over a period of four years. The response of CH4 production potential and methanogenic archaea to climate change was analyzed. We found a relatively high mean annual cumulative CH4 emission of 37.7 g CH4-C m(-2). The dominant contributor to CH4 emission was the thawing period: warmer, longer thawing periods contributed 69.1-88.6% to the annual CH4 budget. Non-thawing periods also contributed, with shorter frozen-thawing periods accounting for up to 18.5% and shorter thawing-freezing periods accounting for up to 8.8%. Over the course of a year, emission peaked in the peak growing season and at onset of thawing and freezing. In contrast, emission did not vary substantially during the frozen period. Daily mean emission was highest during the thawing period and lowest during the frozen period. Diurnal patterns of CH4 emission were similar among the four periods, with peaks ranging from 12:00 to 18:00 and the lowest emission around 00:00. Water table and temperature were the dominant factors controlling CH4 emissions during different thawing-freezing periods. Our results suggest that CH4 emission from peatland will change substantially as CH4 production, microbial composition, and patterns of thawing-freezing cycles change with global warming. Therefore, frequent monitoring of CH4 fluxes in more peatlands and in situ monitoring of methanogenesis and related microbes are needed to provide a clear picture of CH4 fluxes and the thawing-freezing processes that affect them.