Characteristics And Mechanism Of Soil Greenhouse Gases At Different Land Use In The Temperate Steppe Of Inner Mongolia,China

Global change is currently the most concerned scientific issue.The increase of greenhouse gases in the atmosphere is the main cause of global warming.Land use change is one of the main reasons for the increase of greenhouse gas emissions from terrestrial ecosystems.The grassland ecosystem is the largest terrestrial ecosystem in China and has an important impact on climate change.Grazing,mowing and reclamation are the most common management practices for the meadow steppe and affects greenhouse gas exchange.Understanding and grasping the characteristics of human activities on grassland soil greenhouse gas emissions and their impact mechanisms is critical to accurately assessing greenhouse gas emissions from grassland ecosystems,and provides an important scientific basis for the scientific management and sustainable use of grasslands.In this study,the opaque chamber technique and situ gas collection system was used to measure the greenhouse gas fluxes in the surface soil and soil profile at the grazing-exclusion,grazing,mowin and reclamation sites.The main conclusions were summarized as follows.1.The soil CO₂ fluxes have significant daily and seasonal dynamic characteristics for all land-use types.The CO₂ emission fluxes of grazing-exclusion,grazing,mowing,and reclamation sites were 254.47mg m^-2 h^-1,329.38 mg m^-2 h^-1,275.13 mg m^-2 h^-1,490.07 mg m^-2 h^-1.Compared with grazing-exclusion,soil CO₂ emissions for the grazing,mowing,and reclamation sites have increased.Soil CO₂ emission flux has a significant exponential regression relationship with soil temperature（P<0.05）,and a significant linear regression relationship with soil water content（P<0.05）,soil temperature and soil water content are the main controlling factors of soil CO₂ flux.2.The soil CH₄ fluxes have significant seasonal dynamic characteristics.The CH₄ emission fluxes of grazing-exclusion,grazing,mowing,and reclamation were-73.24μg m^-2 h^-1、-78.21μg m^-2 h^-1、-83.63μg m^-2 h^-1、-24.00μg m^-2 h^-1.Compared with grazing-exclusion,CH₄ fluxes have increased at the grazing and mowing sites while decreased in reclamation site.There was a significant positive correlation between the CH₄ flux and soil temperature at the grazing and mowing sites（P<0.05）.The CH₄ flux had a binomial relationship with soil water content at the grazing-exclusion and reclamation sites（P<0.05）.The main control factors for CH₄ flux are soil temperature and soil water content for the grazing-exclusion site.Soil temperature is the main controlling factors of CH₄ flux for the grazing and mowing sites.The main controlling factor of CH₄ flux at the reclamation site is soil water content.3.There is no significant daily and seasonal dynamic characteristics of soil N₂O fluxes.The emission flux of N₂O at the grazing-exclusion,grazing,mowing,and reclamation sites was 333.81μg m^-2 h^-1、27.48μg m^-2 h^-1、26.46μg m^-2 h^-1、34.70μg m^-2 h^-1.Compared with grazing-exclusion,soil N₂O emission fluxes at the grazing and mowing sites have decreased while increased at the reclamation site.There is no correlation between the N₂O flux and soil temperature among the four different land use（P>0.05）.The N₂O flux was positively correlated with soil water content for the grazing-exclusion and grazing sites（P<0.05）,and the soil water content is the main controlling factor of N₂O flux.4.During the spring thawing period,the cumulative amount of CO₂ and N₂O emissions accounted for1.74%-3.25%and 9.25%-12.52%of the total annual emission.The cumulative amount of CH₄ flux only accounts for the 3.58%-4.12%of the annual absorption during the spring thawing period.5.The soil depth of 0-20cm is the main source of the surface CO₂ emission flux at the grazing-exclusion and reclamation sites.The soil depth of 0-30cm is the main source of the surface CO₂ emission flux at the grazing and mowing sites.The CH₄ flux mainly comes from the 0-20cm soil depth,and the N₂O flux mainly comes from the 0-30cm soil depth among the four land-use types.