Growing season methane emission from a boreal peatland in the continuous permafrost zone of Northeast China: effects of active layer depth and vegetation

Boreal peatlands are significant natural sources of methane and especially vulnerable to abrupt climate change. However, the controlling factors of CH4 emission in boreal peatlands are still unclear. In this study, we investigated CH4 fluxes and abiotic factors (temperature, water table depth, active layer depth, and dissolved CH4 concentrations in pore water) during the growing seasons in 2010 and 2011 in both shrub-sphagnum-and sedge-dominated plant communities in the continuous permafrost zone of Northeast China. The objective of our study was to examine the effects of vegetation types and abiotic factors on CH4 fluxes from a boreal peatland. In an Eriophorum-dominated community, mean CH4 emissions were 1.02 and 0.80 mg m(-2) h(-1) in 2010 and 2011, respectively. CH4 fluxes (0.38 mg m(-2) h(-1)) released from the shrub-mosses-dominated community were lower than that from Eriophorum-dominated community. Moreover, in the Eriophorum-dominated community, CH4 fluxes showed a significant temporal pattern with a peak value in late August in both 2010 and 2011. However, no distinct seasonal variation was observed in the CH4 flux in the shrub-mosses-dominated community. Interestingly, in both Eriophorum- and shrub-sphagnum-dominated communities, CH4 fluxes did not show close correlation with air or soil temperature and water table depth, whereas CH4 emissions correlated well to active layer depth and CH4 concentration in soil pore water, especially in the Eriophorum-dominated community. Our results suggest that CH4 released from the thawed CH4-rich permafrost layer may be a key factor controlling CH4 emissions in boreal peatlands, and highlight that CH4 fluxes vary with vegetation type in boreal peatlands. With increasing temperature in future climate patterns, increasing active layer depth and shifting plant functional groups in this region may have a significant effect on CH4 emission.