Effects of Different Land Cover Types on Soil Microbial Biomass Carbon and Nitrogen in the Lower Reaches of Niyang River

[Objectives] To comprehensively and deeply explore the effects of different land cover types in the lower reaches of Niyang River on soil microbial biomass carbon and nitrogen, and to provide a scientific basis for the rational use and sustainable management of land resources in this area. [Methods] Taking the 3 types of land cover (cultivated land, grass land and forest land) in the lower reaches of Niyang River in Tibet as the research object, the contents, distribution characteristics and relationships of soil organic carbon, organic nitrogen, microbial biomass carbon, microbial biomass nitrogen and readily oxidizable organic carbon, and their relationships were studied in 0-10, 10-20, 20-40, 40-60, and 60-100 cm soil depth. [Results] The soil organic carbon content of forest land was higher than that of grass land and cultivated land; the vertical change trend of soil organic carbon content decreased with the increase of depth (P<0.05), and it was mainly concentrated in the soil with a depth of 0-20 cm. The soil organic carbon content was significantly different among forest land, grass land and cultivated land (P<0.05), but there was no significant difference between cultivated land and grass land (P>0.05). The soil organic nitrogen content was significantly different among cultivated land, grass land, and forest land (P<0.05), but there was no significant difference between grass land and forest land (P>0.05). The readily oxidizable organic carbon, microbial biomass carbon and nitrogen in forest land were higher than that in cultivated land and grass land. The change trend of soil readily oxidizable organic carbon, microbial biomass carbon and microbial biomass nitrogen was similar to the change of soil organic carbon content, showing a significant positive correlation. In addition to being subject to land cover, soil microbial biomass carbon and nitrogen content were also subject to the interaction of factors such as soil temperature, humidity, pH and vegetation types. [Conclusions] Changes in land cover significantly affect soil organic carbon and nitrogen, readily oxidizable organic carbon, microbial biomass carbon and nitrogen content.