Investigation Of Soil Nitrogen Fixing Microbial Community In Grassland Ecosystem On Loess Plateau

Grassland makes up 32%of the Loess Plateau’s total area and is a crucial part of the ecosystem there.It is crucial for preserving the region’s ecosystem’s ability to function.In natural ecosystems,nitrogen-fixing bacteria have a unique functional role in converting atmospheric nitrogen into fertilizer for plant uptake and usage,sustaining plant development,and balancing the nitrogen content of the ecosystem.The Loess Plateau grassland ecosystem has been the subject of extensive research on the composition and function of soil microbial communities;however,the distribution characteristics and effects of nitrogen-fixing bacteria are still unknown,which will limit our ability to assess grassland management and the ecological advantages of converting farmland to grassland.This study used the grassland ecosystem of the Loess Plateau as the research object,and it used fluorescence real-time quantitative and amplification sub sequencing technology to analyze the distribution characteristics and driving factors of soil nitrogen fixing bacteria in different vegetation zones（forest zone,Forest steppe zone,grassland zone,grassland desert zone）of the Loess Plateau.The following are the main findings:（1）The four vegetation zones of the grassland differ significantly in terms of plant richness,above and below-ground biomass,and community stability.In comparison to grassland zone and grassland desert zone,the Patrick index and Simpson index of the grassland plant community in the Forest steppe zone were much higher,and the Sheldon index of the grassland desert zone was significantly lower than that of other vegetation zones.For grasslands in various vegetative zones,the Patrick index size ranges from 1.43 to 2.33,the Simpson index from 0.76 to 0.85,and the Sheldon index from 0.70 to 0.76.In comparison to the steppe zone and steppe desert zone,the biomass of the grassland plant community in the Forest steppe zone is much higher.The biomass above and below ground varies from 126 to 221 g.m^-2 and64 to 145 g.m^-2,respectively.In comparison to the Forest steppe zone,the stability of the grassland plant community is substantially lower in the grassland zone and grassland desert zone.The biomass and community stability are as follows:Forest steppe zone follows by forest,then grassland,then grassland desert.（2）The Loess Plateau’s grassland has an abundance of nitrogen-fixing bacteria that ranges from 0.15×10⁸ to 0.29×10⁸ copies.g^-1 dry soil.The abundance of the forest zone,forest steppe zone,and grassland zone differs greatly from that of the grassland desert zone,with the forest zone having the highest abundance and the grassland desert zone having the lowest abundance microorganisms that fix nitrogen in the forest and forest steppe zones.The Shannon diversity index of rare species was1.29 times greater than that of rich species.Rare species diversity is much higher than that of grassland and grassland desert.Azotobacterial the diversity of grassland in different vegetation zones exhibits considerable habitat differences;the diversity is significantly lower than that of rich species.The general,rich,and uncommon communities’makeup is essentially the same in the grassland of the Loess Plateau.Proteobacteria（81.25%）fix nitrogen more abundantly than Cyanobacteria（11.45%）,Firmicutes（3.13%）,and Verrucomycetes（2.65%）in terms of relative abundance.Proteobacteria are significantly more prevalent in the forest,forest steppe,and grassland belts than they are in the grassland desert belt,while cyanobacteria are significantly more prevalent in the grassland and forest steppe than they are in the forest belt.（3）Numerous environmental conditions have an impact on the quantity,diversity of the bacterial communities,and composition of the nitrogen-fixing bacteria in the grassland of the Loess Plateau at the same time.Significantly negative correlations were found between abundance and soil bulk density and clay content,while significant positive correlations were found between abundance and rainfall,soil pH,and total nitrogen.Rainfall,soil pH,and total nitrogen had the strongest correlations with abundance.While the diversity of uncommon species was strongly connected with longitude,rainfall,soil pH,and total nitrogen,the diversity of rich species of nitrogen-fixing bacteria was significantly correlated with species diversity,rainfall,soil pH,and total nitrogen.The most significant influence on the overall makeup of nitrogen-fixing bacterial communities is provided by soil variables,which include above-ground biomass,longitude,total nitrogen content,and soil pH.In conclusion,there is a declining trend in both the diversity and abundance of grassland nitrogen-fixing bacteria on the Loess Plateau from southeast to northwest.The key variables influencing the spread of grassland nitrogen-fixing bacteria communities are rainfall,plant diversification,soil total nitrogen,and pH.Although there are obvious habitat differences between rich and rare groups,which may be closely related to the environmental dependence of nitrogen fixing bacteria species,the diversity of nitrogen fixing bacteria in forest zones and forest steppe zones is higher than that in grassland zones and grassland desert zones.The aforementioned findings can serve as a sound scientific foundation for the evaluation and control of grassland ecosystem functioning on the Loess Plateau.