title: Effect of stocking rate on soil-atmosphere CH4 flux during spring freeze-thaw cycles in a northern desert steppe, China.
abstract: BACKGROUND
  Methane (CH(4)) 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 CH(4) uptake in desert steppes, we investigated soil-atmosphere CH(4) exchange during the winter-spring transition period.
  The 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 CH(4) 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 CH(4) uptake in period I (7.51 µg CH(4)-C m(-2) h(-1)) was significantly lower than uptake in period II (83.07 µg CH(4)-C m(-2) h(-1)). Averaged over 2 years, CH(4) fluxes during the freeze-thaw period were -84.76 µg CH(4)-C m(-2) h(-1) (NG), -88.76 µg CH(4)-C m(-2) h(-1) (LG), -64.77 µg CH(4)-C m(-2) h(-1) (MG) and -28.80 µg CH(4)-C m(-2) h(-1) (HG).
  
  
  CONCLUSIONS
  CH(4) uptake activity is affected by freeze-thaw cycles and stocking rates. CH(4) uptake is correlated with the moisture content and temperature of soil. MG and HG decreases CH(4) uptake while LG exerts a considerable positive impact on CH(4) uptake during spring freeze-thaw cycles in the northern desert steppe in China.
authors.affiliation: College of Ecology and Environmental Science, Inner Mongolia Agricultural University, Huhhot, China. cjwang3@sohu.com
authors.forename: Cheng-Jie
authors.initials: CJ
authors.lastname: Wang
authors.forename: Shi-Ming
authors.initials: SM
authors.lastname: Tang
authors.forename: Andreas
authors.initials: A
authors.lastname: Wilkes
authors.forename: Yuan-Yuan
authors.initials: YY
authors.lastname: Jiang
authors.forename: Guo-Dong
authors.initials: GD
authors.lastname: Han
authors.forename: Ding
authors.initials: D
authors.lastname: Huang
mesh_terms: D000818:Animals; D002681:China; D017753:Ecosystem; D005615:Freezing; D008697:Methane / Q000737:chemistry*; D012756:Sheep / Q000502:physiology; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D008697:Methane