| The study of the biogeographic distributions and its driving factors of the biological groups on Earth are the fundamental key in forecasting the effects of climate change on various types of ecosystems.Soil microbial community play an important role in terrestrial ecosystem,in particular nutrient turnover.However,the mechanism of the soil microbial distributions and its drivers at the regional scales remains poorly understood.The temperate grassland on the Mongolian Plateau is an ideal research area across an integrated gradient of climate(i.e.,arid and semi-arid regions),soil(i.e.,chernozem,Castanozem and Sierozem)and biome types(i.e.,meadow-,typical-,and desert-steppe)in northern China,Inner Mongolia.In our study,we investigated and analyzed spatial distribution pattern of soil microbial biomass and community composition by Phospholipid fatty acid overall 78 sites.We also collected the biotic and abiotic variables,such as soil texture,soil p H,soil bulk density(BD),soil stoichiometry(soil C,N,P),aboveground biomass(AGB),plant species richness(SR),plant stoichiometry(foliar C,N,P),mean annual temperature(MAT),and mean annual precipitation(MAP).The results were as followed:1)The microbial biomass of the 0-10 cm and 10-20 cm layer soils showed significant differences among the three types of grassland(P<0.01).The highest value of soil microbial biomass occurred in meadow grassland,followed by typical grassland,and the lowest was in desert grassland.The ratio of fungal: bacteria in desert grassland is significantly higher than other types of grassland(P<0.05).2)At the regional scale,the microbial community biomass(including total biomass and biomass of major functional groups)at different depths of the soil increased with MAP,SR,AGB,PP,SOC,TN,TP,soil C: N,soil N: P,clay content%,but decreased with MAT,plant N: P,BD,p H,and sand content%(P<0.01).In addition,there was a significant difference between 0-10 cm and 10-20 cm soil layers in response to climate,soil nutrients,texture,and plant community diversity and biomass(P<0.05).3)The direct driving factor of topsoil microbial community was soil properties,especially organic carbon content was the most important factor.With the vertical depth of soil increased,the importance of factors affect the microorganisms turn into the structure of the soil(bulk density).The structural equation models showed that climate was the most critical driving factor affect the spatial pattern of soil microbial communities in temperate grassland in Inner Mongolia.But this effect of climate was indirectly affected via plant and soil organic carbon.However,climatic factors can also directly regulate the distribution of arbuscular mycorrhizal fungi in the subsoil.We didn't find significant direct effect between plants and soil microbial biomass,and the effects of plants mainly expressed by soil SOC indirectly.We also found the driving factor of the Saprophytic fungi: bacterial ratio(F: B)in topsoil(0-10cm)was organic carbon,but in the subsoil(10-20cm)was p H.In conclusion,the spatial distribution patterns of soil microbial communities in temperate grasslands in Inner Mongolia has a similar pattern to that of vegetation(productivity,biodiversity),which is mainly due to the climate(temperature and precipitation pattern)driving the spatial pattern of vegetation and soil,and further affect the distribution pattern of soil microorganisms.However,it should be noted that the spatial patterns of soil microbes and their response to environmental factors have significant differences in different soil depths.This may be of great significance for Inner Mongolia grasslands affected by human activities over a long period of time.Human activities interfere with the impact on the surface soil is greater,and may be superimposed on the impact of natural environmental factors such as climate and affect the soil microbial community,in future should increase this research. |
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