Soil methane uptake by grasslands and forests in China

Sinks of methane (CH4) become highly variable due to both human activity and climate change. An urgent need therefore exists to budget key sinks of CH4, such as forests and grasslands. In this study, CH4 uptake of forests and grasslands in China was first reviewed and then estimated based upon the review itself. Total uptake from the two CH4 sinks were 1.323 Tg CH4 yr−1 in China (ranging from 0.567 to 2.078 Tg CH4 yr−1), lower than a previous estimate in China (2.56 Tg CH4 yr−1). Among the uptake, 0.650 Tg CH4 yr−1 (ranging from 0.168 to 1.132 Tg CH4 yr−1) was consumed by grasslands and 0.675 Tg CH4 yr−1 (ranging from 0.399 to 0.946 Tg CH4 yr−1) by forests. The largest CH4 uptake of grasslands was found in the Qinghai-Tibetan Plateau High-Frigid Domain, which consumed 0.284 Tg CH4 yr−1, about 44% of the whole uptake of grasslands in China. The greatest CH4 uptake (0.553 Tg CH4 yr−1) of forests took place in Eastern Humid and Semi-humid Domain of the country, which was about 82% of the total annual CH4 uptake of forests in China. With forests and grasslands taken together, Eastern Humid and Semi-humid Domain was the largest CH4 consumer, taking up about 0.715 Tg CH4 yr−1, accounting for 82% of the whole forest uptake and 25% of the whole grassland uptake in China. On the ecoregion scale, due to extensive forest distribution and longer growing season, Southern Asia monsoon broadleaf forest ecoregion was the greatest CH4 uptake (0.320 Tg CH4 yr−1) of forests and grasslands in China, consuming more CH4 than the Northeastern Arid and Semi-arid Domain combined. Our results indicated that forests and grasslands are not constant sinks of CH4 but decreasing ones influenced by climate change and anthropogenic activity. More field data, mechanism understanding and process-based models could help better estimate and understand CH4 uptakes of forests and grasslands in China.