Soil microbial biomass could be used as significant biological indicator to reflect soil quality and ecological restoration of sandy land. However, little was known on the relationship between human trampling to biocrusts and soil microbial biomass in desert areas. To explore the effects of human trampling to biocrusts on soil microbial biomass, sand soil under human trampling to biocrusts was served as the research object and soil underneath non-trampling biocrusts was the reference in artificial and natural vegetation areas at the southeastern edge of the Tengger Desert. Trampling to biocrusts was divided into three levels depending on the trampling degree to biocrusts:non-trampling, medium trampling and severe trampling, respectively. Soil samples were taken from the three trampling degrees in 0~5 cm and 5~15 cm soil depth, respectively, and microbial biomass carbon and nitrogen were measured. The results showed that human trampling to cyanobacteria-lichen and moss crusts could reduce soil microbial biomass carbon and nitrogen. Moreover, soil microbial biomass carbon and nitrogen decreased as the trampling degree to biocrusts increased. Severe trampling to cyanobacteria-lichen and moss crusts significantly declined soil microbial biomass carbon and nitrogen (P<0.05). The loss of soil available phosphorus, available nitrogen, total phosphorus and total nitrogen act as the important factors which caused the reduction of soil microbial biomass carbon and nitrogen. In addition to the trampling degree, soil microbial biomass carbon and nitrogen after human trampling to biocrusts are also significantly influenced by the successional stage of crusts (P<0.05). Soil microbial biomass carbon and nitrogen under trampled moss crusts significantly higher than trampled cyanobacteria-lichen crusts. This indicated that late-stage moss crusts had more stronger anti-interference capability than early-stage cyanobacteria-lichen crusts(P<0.05). In addition, there was a consistent law of soil microbial biomass carbon and nitrogen under biocrusts no matter how seasons change, follow orders:non-trampling > medium trampling > severe trampling. Moreover, there were seasonal changes of soil microbial biomass under trampling biocrusts, follow orders:summer > autumn > spring > winter. Therefore, trampled biocrusts could decrease soil microbial biomass in artificial and natural vegetation areas at southeastern edge of the Tengger Desert, indicating the degradation of soil and the desert ecosystem. The results showed that the protection to biocrusts could recover the desert ecosystems in desert areas.
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