Bacterial Diversity And Its Seasonal Variation Characteristics Among Different Biological Soil Crusts In The Shapotou Region Of Southeast Tengger Desert

Biological soil crusts(BSCs)are important components of the surface soil and accounts for 70% of the bare soil in arid and semi-arid regions.The development,colonization and succession of BSCs are important health indicators in desert and sandy ecosystems.According to the dominant species,BSCs are generally divided into three main succession stages: algae crust,lichen crust and moss crust.With the development and succession of biocrusts,lichens and mosses have gradually become the dominant groups of BSCs,and the microbial community structure is also constantly changing.In this study,ammonium nitrogen,nitrate nitrogen,organic carbon and total nitrogen were determined in the algal crust,moss crust and their sublayer soil widely distributed in the southeastern Tengger Desert.The effects of these four chemical indicators,biocrust types and seasonal dynamics on the bacterial diversity and species composition are analyzed.The main conclusions are as follows:(1)The soil particle size composition of different types of biocrusts is significantly different.With the development and succession of biocrusts,the content of clay,powder and very fine sand in the moss biocrust and its sublayer soil is higher than that of the algal crust and its sublayer soil.(2)With the development and succession of biocrusts,the content of organic matter,total nitrogen and ammonium nitrogen gradually increase,while the content of nitrate nitrogen decreases.Along with seasonal dynamic,the organic matter content is highest in winter,and decreases in the order of spring,summer,and autumn.The content of nitrate nitrogen is highest in spring,and decreases in the order of autumn,summer and winter.The content of ammonium nitrogen is the highest in autumn,and decreases in the order of summer,spring and winter.(3)The results showed that the bacterial abundance of four types of biocrusts had similar changes,that is,the bacterial community richness indexes of Chao,Ace and Sobs in summer in the algal biocrust,moss biocrust and their sublayer were significantly lower than those in the other three seasons.(4)The bacterial communities of the four biocrust types mainly include Proteobacteria,Actinobacteria,Chloroflexi,Acidobacteria,Cyanobacteria,Bacteroidetes,Gemmatimonadetes,Planctomycetes,Patescibacteria,Armatimonadetes,Verrucomicrob ia,Deinococcus-Thermus,but there are seasonal dynamics.(5)Proteobacteria and Actinobacteria in the algal biocrust are positively correlated with nitrate nitrogen and organic matter,while Chloroflexi,Acidobacteria,Cyanobacteria are positively correlated with organic matter,ammonium nitrogen and total nitrogen.Proteobacteria and Actinobacteria in the sublayer of algal biocrusts are positively correlated with nitrate nitrogen and ammonium nitrogen,and Gemmatimonadetes are positively correlated with nitrate nitrogen and total nitrogen.Chloroflexi and Acidobacteria are positively related to organic matter and total nitrogen.Chloroflexi and Acidobacteria in moss biocrusts are positively correlated with ammonium nitrogen and total organic nitrogen.Proteobacteria,Actinobacteria and Cyanobacteria are positively related to nitrate nitrogen.The five dominant phyla in the sublayer of the moss biocrust,mainly including Actinobacteria,Gemmatimonadetes,Proteobacteria,Chloroflexi and Acidobacteria,are positively correlated with ammonium nitrogen and total organic nitrogen.