Effect of Long-term Fencing and Grazing Exclusion on the Grassland Soil Organic and Microbial Carbons of Middle Tianshan Mountain

Grassland degradation occurs due to the long-term heavy grazing.The most common rehabilitation methods include fencing,supplemental seeding,fertilizer application and etc.Three types of grassland fenced for long-term(26 years)grazing exclusion in Middle Tianshan Mountains was sampled for analyzing the long-term effect on both soil organic and microbial carbons.The analysis of organic carbon adopts conventional method;and we use Chloroform fumigation extraction-TOC method to measure microbial carbon to mainly analyze the soil samples in the soil profile and the surface soil.The results indicated that organic carbon content in subsoil outside the fence(under the condition of free grazing)in descending order is:alpine meadow(165.29 g.kg-1) alpine meadow steppe(98.37 g.kg-1) alpine steppe(83.54 g.kg-1);whereas soil microbial carbon content:alpine meadow steppe(181.70 mg.kg-1) alpine meadow(146.37 mg.kg-1) alpine steppe(43.06 mg.kg-1).With the treatment of fencing and grazing exclusion,organic carbon content in subsoil of alpine meadow,alpine meadow steppe and alpine steppe increased by 11.37%,3.26% and 2.21% respectively;whereas microbial carbon content increased by 2.89% and 12.04% in alpine meadow steppe and alpine meadow respectively while decreased by 40.36% in alpine steppe.In terms of soil section inside and outside the fenced areas,soil organic carbon and microbial carbon contents both decreased with increase of soil depth,so did Cmic/Corg.Microbial carbon content showed a very significant negative correlation with available K and total P in soi(l P0.01),a very significant positive correlation with available P(P0.01),a significant positive correlation with organic carbon,total N and total K in soi(l P 0.05),and a positive correlation with available N in soil,but not significantly.With the analysis,this paper can provide basis for improving the grassland carbon sequestration potential and reforming degraded grassland.