Effect Of Grazing Exclusion On Soil Organic Carbon And Soil Bacterial Diversity In Sagebrush Desert

The soil organic carbon and soil bacterial diversity in sagebrush desert on northern slope of Tianshan Mountains were measured.Using correlation analysis,redundancy analysis(RDA)and structural equation model(SEM)method aimed to clarify the general law of soil organic carbon and bacterial diversity in the response of sagebrush desert grassland after grazing exclusion.We analyze the influencing factors of soil organic carbon and bacterial diversity,and explore the relationship among soil organic carbon and bacterial diversity.To provide a certain theoretical basis for understanding the restoration of degraded sagebrush desert grassland soil.The main results are as follows:(1)After grazing exclusion,the above-ground biomass of sagebrush desert grassland increased significantly by 65.99%?246.66%,and the below-ground biomass increased by65.56%?151.89%,and it was mainly concentrated in the 0-5 cm soil layer.The litter biomass accumulation effect is not significant(P>0.05).(2)After grazing exclusion,soil water content and total phosphorus content(33.45% and18.87%)showed significantly reduces in Xinyuan sagebrush desert grassland,while the electrical conductivity was significantly increased by 347.87%,But there was no significant change in other plots(P>0.05).There was no change in soil bulk density,p H,total nitrogen content,and microbial biomass carbon in all plots(P>0.05).After grazing exclusion,the microbial biomass nitrogen and microbial biomass phosphorus of the Qitai plot were significantly reduced by 31.80% and 42.05%,while the microbial biomass nitrogen of the Hutubi plot was significantly increased by 27.90%,and the microbial biomass P of the Bole plot was significantly increased by 43.02%;The changes of microbial biomass N and P in other plots were not significant(P>0.05).(3)Grazing exclusion decreased soil organic carbon content and organic carbon storage in0-50 cm of sagebrush desert grassland,respectively,and the performance of different plots was not consistent.SEM showed that both vegetation characteristics and soil characteristics had direct or indirect effects on SOC.The direct path coefficient of soil property on SOC was the largest(-0.45),while the direct path coefficient of vegetation biomass on SOC was the smallest(0.08).Grazing enhanced the transformation of vegetation,soil and organic carbon,while grazing exclusion slowed this conversion.(4)The dominant phyla of soil bacteria in 0-10 cm sagebrush desert grassland were Actinobacteria,Proteobacteria,Acidobacteria,and Chloroflexi.The number of bacteria,diversity index did not increase significantly,but changed the proportion of each dominant phyla.After grazing exclusion,Actinobacteria increased by 17.35%,Proteobacteria decreased by 25.42% and Firmicutes decreased by 89.04%.(5)SEM showed that the direct effect path coefficient of plant biomass on soil bacterial diversity was the highest(-0.34),while the direct effect path coefficient of vegetation diversity on soil bacterial diversity was the lowest(-0.08).Grazing exclusion reduced the direct impact of vegetation and soil on soil bacterial diversity,but increased the indirect impact on soil bacterial diversity.(6)Among the effects of many factors on organic carbon,SEM showed that soil property hadthe greatest direct impact on organic carbon(-0.97),followed by microbial biomass(0.83).The path coefficient of direct effect of vegetation biomass on 0-10 cm soil organic carbon was-1.72,while the path coefficient of direct effect of microbial biomass on soil organic carbon decreased from 0.83 to 0.32.Soil organic carbon was negatively correlated with vegetation diversity and microbial diversity,and positively correlated with microbial biomass and soil property;grazing exclusion changed the regulation of vegetation biomass and soil property on organic carbon.In general,the effects of grazing exclusion on soil property and soil bacterial diversity were not significant,but grazing exclusion could significantly increased above-ground and below-ground biomass.Grazing exclusion decreased soil organic carbon content and storage.SEM showed that the decrease of soil organic carbon content may be caused by the increase of plant biomass after grazing exclusion,it should be further studied.