Characteristics Of Soil Protist And Autotrophic Community And Their Drivers In Grasslands Of The Tibetan Plateau

Protists and autotrophic microorganisms,as important components of soil microbial communities,play an important role in regulating nutrient cycling and carbon fixation in terrestrial ecosystems.The Tibetan Plateau grassland is a typical representative of fragile ecosystems in arid regions.Plant growth and diversity have been restricted by multiple environmental pressures such as drought and high cold for a long time.The impact of soil microbial communities on ecosystem functions is more significant.However,little is known about the distribution patterns and driving factors of protists and autotrophic microorganisms in grassland soils on the Tibetan Plateau,which greatly limits our understanding of the functions and functions of soil protists and autotrophic microorganisms in the Tibetan Plateau and understanding of climate change responses.This study was conducted to investigate the community characteristics and environmental driving mechanisms of soil protists and autotrophic microorganisms and their response to human grazing activities in alpine grasslands(meadows,steppe and desert)spanning 1200 km across the Tibetan Plateau,by applying high-throughput sequencing technology.The results showed that:(1)The α diversity of the soil protist community decreased significantly along the gradient of meadow,steppe and desert,and the community structure changed significantly.The structural equation model(SEM)showed that precipitation indirectly dominated the diversity of protist communities directly by affecting plant and soil factors,while grazing indirectly reduced the diversity of protists mainly by affecting aboveground plant biomass.Variance partitioning analysis(VPA)showed that the individual contribution rate of climatic factors(5.1%)to the protist community structure was greater than that of soil(2.8%)and plant factors(0.8%).Random forests showed that precipitation was the most important driver of protist community structure.In addition,the soil protist communities were composed of Cercozoa,Ciliophora,Chlorophyta and Ochrophyta.Among them,the relative abundance of Ciliophora increased significantly from meadow(24.87%)to steppe(28.41%)and desert(41.82%),while the relative abundance of Chlorophyta decreased gradually from meadow(28.88%),steppe(15.42%)to desert soil(7.99%).(2)The α diversity of autotrophic microorganisms in steppe soils was significantly higher than that in meadow and desert soils.SEM results showed that precipitation was the most important driver of autotrophic microbial richness and community structure,followed by plant richness and soil pH.There was no significant correlation between soil nutrients(total organic carbon,ammonium nitrogen,and dissolved nitrogen)and the richness of autotrophic microorganisms.Autotrophic microorganisms were mainly Actinobacteria and Proteobacteria,among which Actinobacteria accounted for 31.83%of the relative abundance in meadow soils,and increased significantly in the transition from steppe(52.00%)to desert(60.25%).The relative abundance of Alphaproteobacteria decreased gradually from meadow(42.83%)to steppe(23.33%)to desert(21.97%).(3)Grazing significantly affected the α diversity,community structure and composition of soil protist communities.Grazing significantly reduced the α-diversity of protist communities in meadow soils and altered the correlations of protist community diversity with precipitation,aboveground plant biomass,and soil nutrients.Grazing significantly changed the community structure of protists in meadow and steppe soils,significantly decreased the relative abundance of ciliates in meadow and steppe soils,and significantly increased the relative abundance of ciliates in steppe soils.In addition,grazing had no significant effect on the α diversity,community structure,and composition of the autotrophic microorganisms.The above results suggested that precipitation determines the diversity and community structure of soil protists and autotrophs,and protists are more sensitive to environmental changes caused by grazing than autotrophs.Thus,protists can serve as good environmental indicators.The results of this study can provide basic data for a better understanding of the relationship between soil microorganisms,climate change and human activities,and provide a theoretical basis for the protection and utilization of alpine grasslands.