Diel and Seasonal Dynamics of Ecosystem‐Scale Methane Flux and Their Determinants in an Alpine Meadow

Temporal variations of methane flux (FCH 4 ) and its underlying mechanisms still remain poorly understood. To quantify diurnal and seasonal patterns of FCH 4 and investigate its determinants, we monitored FCH 4 using eddy covariance in an alpine meadow on the Qinghai‐Tibetan Plateau, China, from June 2015 to December 2016. As a strong CH 4 sink, the alpine meadow on the Qinghai‐Tibetan Plateau consumed 0.41 ± 0.04 Tg CH 4 /year. There was an obvious diurnal pattern with more CH 4 uptakes during the nighttime than the daytime for both growing and nongrowing season. The diurnal FCH 4 during the growing and nongrowing season were positively correlated with air temperature (Ta), volumetric water content, friction velocity (u * ), and vapor pressure deficit. The growing season FCH 4 showed a significant quadratic polynomial relationship with the canopy conductance (G w ) and gross primary production). FCH 4 was significantly higher in the growing season than in the nongrowing season. The seasonal FCH 4 was negatively correlated with soil temperature and net radiation (Rn) but not with volumetric water content and gross primary production. Ridge regression models indicated that Ta and u * explained 83% of the variation in the diel dynamics of FCH 4 during the growing season and explained 72% of the variation during the nongrowing season. Rn accounted for 49% of variations of FCH 4 at the seasonal scale. The temporal patterns and the environmental controlling factors revealed in this study may improve model parameterization for biosphere‐atmosphere CH 4 exchange simulation as well as the methane budget estimation.