Considerable methane uptake by alpine grasslands despite the cold climate: in situ measurements on the central Tibetan Plateau, 2008–2013

The uptake of CH 4 by aerate soil plays a secondary role in the removal of tropospheric CH 4 , but it is still highly uncertain in terms of its magnitude, spatial, and temporal variation. In an attempt to quantify the sink of the vast alpine grasslands (1 400 000 km 2 ) of the Tibetan Plateau, we conducted in situ measurements in an alpine steppe (4730 m) and alpine meadow (4900 m) using the static chamber and gas chromatograph method. For the alpine steppe, measurements (2008–2013) suggested that there is large interannual variability in CH 4 uptake, ranging from −48.8 to −95.8 μg CH 4  m −2  h −1 (averaged of −71.5 ± 2.5 μg CH 4  m −2  h −1 ), due to the variability in precipitation seasonality. The seasonal pattern of CH 4 uptakes in the form of stronger uptake in the early growing season and weaker uptake in the rainy season closely matched the precipitation seasonality and subsequent soil moisture variation. The relationships between alpine steppe CH 4 uptake and soil moisture/temperature are best depicted by a quadratic function and an exponential function ( Q 10  = 1.67) respectively. Our measurements also showed that the alpine meadow soil (average of −59.2 ± 3.7 μg CH 4  m −2  h −1 ) uptake less CH 4 than the alpine steppe and produces a similar seasonal pattern, which is negatively regulated by soil moisture. Our measurements quantified – at values far higher than those estimated by process‐based models – that both the alpine steppe and alpine meadow are considerable CH 4 sinks, despite the cold weather of this high‐altitude area. The consecutive measurements gathered in this study also highlight that precipitation seasonality tends to drive the interannual variation in CH 4 uptake, indicating that future study should be done to better characterize how CH 4 cycling might feedback to the more extreme climate.