Ecological C:N:P Stoichiometry Of Soil Microorganisms And Its Driving Factors In Grassland Of Inner Mongolia

Microbial C:N:P stoichiometry and its driving factors play crucial roles in understanding the balance and cycling of chemical elements in ecological interactions.However,little is known about pattern and variation in the Inner Mongolian grasslands due to the lack of the comprehensive field investigations.In this study,we firstly optimized the fumigation time and concentration of extract in alkaline soils.In addition that,this study through the methods of combining the field investigation and indoor experiment,to study the pattern and variation of soil microbial C:N:P stoichiometry in Inner Mongolian grassland transect,and revealed the relationships between the main driving factors(climate,soil and abiotic factors)and the C:N:P ratio in soil microbial biomass.In order to provide the scientific bases for the precise determination of soil microbial biomass carbon(MBC),9 chloroform fumigation time and 2 K2SO4 concentrations were performed to explore the optimal fumigation time and extracted concentration for alkaline soil MBC determination.The following conclusions:(1)In alkaline soils,fumigation time is significantly correlated with soil organic matter(SOM)concentration.Higher SOM concentration needs longer fumigation time to obtain stable MBC content.Fumigation time for high SOM(?60g·kg-1)is at least 24 hours,while that of middle and low SOM(?40g·kg-1)is at least 18 hours.(2)SOM concentration influences K2SO4 extraction efficiency,the high and middle SOM concentration soils need 0.5 mol·L-1K2SO4 solution to extract,0.25 mol·L-1 1K2SO4 solution is enough to extract the MBC contents for low SOM soil.Based on the data from 216 plots in 72 sites in grassland transect of northern China,this study aimed to find out the patterns of microbial C:N:P stoichiometry in the topsoil and subsoil along the environmental gradient,and identify the driving factors of microbial C:N:P stoichiometry by structural equation model.The main results were summarized as following:(1)The microbial C:N:P ratios is 66:10:1 in the Inner Mongolian grassland,and similar microbial C:N:P stoichiometry patterns is found in both evaluated soil layers(66:9:1).The ANOVA results indicate the microbial N:P ratio significantly differed among steppe?with the following descending order:desert steppe>typical steppe>meadow steppe.However,no significant differences are observed in the microbial C:N and C:P ratios.(2)The microbial C:N and N:P ratios show a certain degree of latitude change.In the topsoil,the microbial C:N ratio increase with the latitude(P<0.01)while the microbial N:P ratio decrease with the latitude(P<0.05).In the subsoil,positive relationship is found between the microbial C:N ratio and the latitude,but the weak association is found between the microbial N:P ratio and the latitude.No or weak associations are found between the micrbial C:P ratio and the latitude in different soil layers.(3)Among all factors,total phospholipid fatty acids(PLFAs)exclusively controll the microbial C:N:P stoichiometry in both soil layers.Similar factors that drive the microbial C:N(aridity index(AI),plant aboveground biomass(AGB))and C:P(soil C:P ratio)ratios are found at both soil depths,and the effects of those factors dilute in the subsoil.Moreover,structural equation modeling reveal that the F:B ratio and sand percentage mainly impact the microbial N:P ratio in the topsoil,while the soil pH and the total PLFAs exert positive effects in the subsoil.In conclusion,we identified the drivers of microbial C:N:P stoichiometry in the Inner Mongolian grassland and the effects of relationships among climatic,edaphic and biotic factors along environmental gradients.The result provided a sight for understanding the chemical element balance and nutrient cycling of grassland soils in Inner Mongolia under the background of global change.