Methane emissions from an alpine wetland on the Tibetan Plateau: Neglected but vital contribution of the nongrowing season

The vast wetlands on the Tibetan Plateau are expected to be an important natural source of methane (CH₄) to the atmosphere. The magnitude, patterns and environmental controls of CH₄ emissions on different timescales, especially during the nongrowing season, remain poorly understood, because of technical limitations and the harsh environments. We conducted the first study on year-round CH₄ fluxes in an alpine wetland using the newly developed LI-COR LI-7700 open-path gas analyzer. We found that the total annual CH₄ emissions were 26.4 and 33.8 g CH₄ m^-2 in 2012 and 2013, respectively, and the nongrowing season CH₄ emissions accounted for 43.2-46.1% of the annual emissions, highlighting an indispensable contribution that was often overlooked by previous studies. A two-peak seasonal variation in CH₄ fluxes was observed, with a small peak in the spring thawing period and a large one in the peak growing season. We detected a significant difference in the diurnal variation of CH₄ fluxes between the two seasons, with two peaks in the growing season and one peak in the nongrowing season. We found that the CH₄ fluxes during the growing season were well correlated with soil temperature, water table depth and gross primary production, whereas the CH₄ fluxes during the nongrowing season were highly correlated with soil temperature. Our results suggested that the CH₄ emission during the nongrowing season cannot be ignored and the vast wetlands on the Tibetan plateau will have the potential to exert a positive feedback on climate considering the increasing warming, particularly in the nongrowing season in this region.