Abstract
BackgroundMethane (CH4) uptake by steppe soils is affected by a range of specific factors and is a complex process. Increased stocking rate promotes steppe degradation, with unclear consequences for gas exchanges. To assess the effects of grazing management on CH4 uptake in desert steppes, we investigated soil-atmosphere CH4 exchange during the winter-spring transition period.Methodology/Main FindingThe experiment was conducted at twelve grazing plots denoting four treatments defined along a grazing gradient with three replications: non-grazing (0 sheep/ha, NG), light grazing (0.75 sheep/ha, LG), moderate grazing (1.50 sheep/ha, MG) and heavy grazing (2.25 sheep/ha, HG). Using an automatic cavity ring-down spectrophotometer, we measured CH4 fluxes from March 1 to April 29 in 2010 and March 2 to April 27 in 2011. According to the status of soil freeze-thaw cycles (positive and negative soil temperatures occurred in alternation), the experiment was divided into periods I and II. Results indicate that mean CH4 uptake in period I (7.51 µg CH4–C m−2 h−1) was significantly lower than uptake in period II (83.07 µg CH4–C m−2 h−1). Averaged over 2 years, CH4 fluxes during the freeze-thaw period were −84.76 µg CH4–C m−2 h−1 (NG), −88.76 µg CH4–C m−2 h−1 (LG), −64.77 µg CH4–C m−2 h−1 (MG) and −28.80 µg CH4–C m−2 h−1 (HG).Conclusions/SignificanceCH4 uptake activity is affected by freeze-thaw cycles and stocking rates. CH4 uptake is correlated with the moisture content and temperature of soil. MG and HG decreases CH4 uptake while LG exerts a considerable positive impact on CH4 uptake during spring freeze-thaw cycles in the northern desert steppe in China.
Highlights
Methane (CH4) is the second most important long-living greenhouse gas (GHG) after carbon dioxide (CO2)
The Intergovernmental Panel on Climate Change (IPCC) reported that global warming potentialweighted emissions of GHG increased by approximately 70% from 1970 to 2004, including emissions of CH4 which have risen by about 40%
Mean CH4 fluxes were significantly increased in period II (283.07 mg CH4-C m22 h21) compared to period I (27.51 mg CH4-C m22 h21) (Figure 2B)
Summary
Methane (CH4) is the second most important long-living greenhouse gas (GHG) after carbon dioxide (CO2). The Intergovernmental Panel on Climate Change (IPCC) reported that global warming potentialweighted emissions of GHG increased by approximately 70% from 1970 to 2004, including emissions of CH4 which have risen by about 40%. It has been reported that in Inner Mongolian grasslands grazing changes soil moisture holding capacity, which in turn affects GHG emissions [4,5,6]. Current estimates for annual exchange rates of CH4 between steppe soils and the atmosphere are still uncertain. To combat this uncertainty, CH4 exchange should be observed during the winter and winter-spring transition period in Inner Mongolian steppes. To assess the effects of grazing management on CH4 uptake in desert steppes, we investigated soil-atmosphere CH4 exchange during the winterspring transition period
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