Land-use types and management practices of temperate semiarid steppes may affect soil sink activity for atmospheric methane (CH4). Most previous studies related to CH4 have focused primarily on the growing season with only a few studies evaluating CH4 fluxes throughout the entire year. With CH4 exchange largely undocumented during the non-growing season, the annual CH4 uptake in different land-use types under various management practices is uncertain. The aim of this study was to investigate the annual variation of CH4 fluxes from four land-use types (ungrazed grassland, moderately grazed grassland, perennial pasture and cropland), which are the dominant land-use types in the agro-pastoral region of northern China. Fluxes of CH4 were measured throughout the year in four land-use types using a mobile greenhouse gas analyzer. Results showed that soils were a sink for atmospheric CH4 throughout the year for all land-use types. Annual CH4 uptake patterns were similar (but with quite different magnitudes) for all land-use types with low, spiky uptake during the two freeze-thaw periods, low and constant uptake during the frozen period and highly variable uptake with some emission events during the growing season. Seasonality of CH4 uptake was related to monthly mean temperature and precipitation. Monthly mean temperature and precipitation explained 56% (range: 40-83%) of the variability in monthly cumulative soil CH4 uptake. Annual CH4 uptake across all land-use types averaged 3.9 +/- 0.3 kg C ha(-1) yr(-1) (range: 1.0-10.2). CH4 uptake during the non-growing season represented about 50% (range: 41-59%) of annual CH4 uptake for the grassland types and 21% (range: 20-22%) for the cropland and perennial pasture land-use types. Moderate grazing (stocking rate 1.43 sheep ha(-1) yr(-1)) significantly increased annual CH4 uptake by 78% (P < 0.05) compared to ungrazed grassland. The highest annual CH4 uptake was observed for cropland (10.2 +/- 0.2 kg C ha(-1) yr(-1)), followed by 2.7 kg +/- 0.1C ha(-1) yr(-1) for perennial pasture. Our results documented year-long CH4 fluxes in four important land-use types in the expansive agro-pastoral region of northern China and contribute to our understanding of soil uptake levels of atmospheric CH4. (C) 2015 Elsevier Ltd. All rights reserved.
