In situ measurements and meta-analysis reveal that land-use changes combined with low nitrogen application promote methane uptake by temperate grasslands in China

摘要

Methane (CH_4) oxidation in well-aerated grassland soils is an important sink for atmospheric CH_4, which can be largely modified by land-use changes. However, the impacts of land-use changes (i.e., from native grasslands to artificial grasslands (AG) and croplands (CL)) on soil CH_4 uptake in China remain uncertain. Therefore, the 2-year CH_4 flux was measured from 3 land-use types, including heavily grazed steppe (HG, control), AG, and CL, in the agro-pastoral ecotone of Northern China to elucidate this impact. Moreover, a meta-analysis was conducted to elucidate this effect across Chinese grasslands. The results showed that the land-use types could not change the seasonal patterns but significantly (p < 0.05) influenced the strength of soil CH_4 uptake. The mean annual CH_4 uptake followed the decreasing order of 14.7 ± 0.48 (mean ± 1 standard error) (CL), 3.28 ± 0.09 (AG), and 1.24 ± 0.07 kg CH_4-C ha~(-1) yr~(-1) (HG) in 2012-2014. This spatial variation pattern was linear and negatively (n = 6, r_(adj.)~2= 0.73, p < 0.05) associated with the annual mean soil water-filled pore space. Non-growing season CH_4 uptake contributed 22-46% to the annual CH_4 uptake across land-use types. The meta-analysis also confirmed that the land-use changes significantly (p < 0.05) promoted the annual soil CH_4 uptake in temperate grasslands in China. This increased uptake is primarily related to the significant (p < 0.05) decrease in the soil water contents and the increase in the sand contents due to the land-use changes. Furthermore, nitrogen application not exceeding 100 kg N ha~(-1) yr~(-1) in these N-limited ecosystems significantly (p< 0.05) promoted soil CH_4 uptake. Collectively, our study demonstrated that land-use changes combined with low N application promoted soil CH_4 uptake in the temperate grasslands of China.