Methane (CH4) emission was measured from an open fen on the Zoige Plateau (3500 m a.s.l.) (the eastern edge of the Qinghai- Tibetan Plateau) during two winters of 2006 and 2007. Three dominant plant stands, including Carex muliensis Hand-Mazz. (CM), Eleocharis valleculosa Ohwif. setosa (Ohwi) Kitagawa.(EV) and Kobresia tibetica Maxim (KT) were chosen to be monitored. Winter CH4 emissions were roughly estimated to be 0.94 mg CH4 m–2 h–1. High spatialtemporal variations of the emission were found in this fen (the sequence of CM> EV> KT; 0.63 and 1.24 mg CH4 m–2 h–1 for 2006 and 2007, respectively). Factors involved in the spatial-temporal variation were: 1) water table in summer determining the winter amount of “old” CH4 stored in peat; 2) ice layer determining the release of CH4; 3) plant growth determining both the quantity of CH4 stored in peat and available substrates for CH4 production in winter. However, due to the homogeneity of freezing in winters, predictive factors such as plant growth and water table in summer could contribute more to winter CH4 emission than in situ freezing conditions. Considering that plant growth and water table are also the key factors controlling the spatial-temporal variation of CH4 emission in summer, we therefore suggested that winter CH4 emission represents the “inertia” of summer CH4 emission.
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