Longitude gradient changes on plant community and soil stoichiometry characteristics of grassland in Hulunbeir Community structure and diversity of soil denitrifying bacteria of the nirK gene type under different vegetation restoration patterns in the Hulunbeier Sandy Land, Inner Mongolia A study on early warning of grassland fire disaster risk in Hulunbeier The study of soil microbial biomass and soil enzyme avtivity on different grassland in Hulunbeier, Inner Mongolia