Effect Of Controlled Precipitation On Soil Bacterial Community In Desert Steppe Of Western Loess Plateau

In the context of climate change,the global and regional precipitation patterns will change.Precipitation is an important source of water in arid and semi-arid ecosystems and a key driver of biological processes at different spatial and temporal scales.As the main driver of earth material circulation,soil bacterial community has not been clearly understood due to its complex structure and the limitations of research methods and research scales.Desert steppe in the western Loess Plateau,as a typical transitional vegetation type between steppe and desert,plays an important role in maintaining the stability of regional ecosystem.However,because of the semi-arid area,the vegetation is sparse and the soil erosion is serious,so the ecosystem is very fragile.Therefore,the study on the effect of precipitation change on soil bacterial community in desert steppe on the western Loess Plateau can provide data support for evaluating the response mechanism of soil carbon pool dynamics to precipitation change in desert steppe,and provide theoretical basis for the management of desert steppe ecosystem.This study used in the field distribution of the loess plateau in the western desert grassland precipitation controlled trial,set up five precipitation gradients(precipitation reducing 40%,precipitation reducing 20%,contrast,add precipitation 20%,add precipitation 40%),using high-throughput sequencing technologies to determine the species composition and diversity of soil microbial communities,the integrated use of analysis of variance,Kruskal-Walli test,LEf Se multistage species difference discriminant analysis,Spearman correlation analysis and structural equation model analysis methods,to study the effects of precipitation change on desert grassland soil bacterial community composition,diversity,plants and soil characteristics and its mechanism.The main research results are as follows:(1)There were significant differences in aboveground biomass,coverage and density under different control precipitation conditions(P<0.05),but there were no significant differences in plant richness,Shannon index and height(P>0.05).Aboveground biomass under 20% precipitation reduction gradient was significantly lower than that under 40% precipitation increase gradient.The coverage under 40%reduced precipitation was significantly lower than that under 20% increased precipitation.The density under 40% precipitation reduction gradient was significantly lower than that of the control and other gradients.The results showed that the precipitation change could affect the growth of plant community,and the extreme drought had more obvious inhibitory effect on the growth of plant community,while the precipitation change had no obvious effect on the diversity and height of plant community(P>0.05).Under different control precipitation conditions,there were significant differences in soil available P and electrical conductivity(P<0.05),and the available P was significantly accumulated under the treatment of 40% water reduction.(2)There was no significant difference in soil microbial biomass carbon under different control precipitation conditions(P>0.05),and it showed a certain increasing trend with the increase of precipitation.Under control precipitation condition,the dominant bacteria in the community were Actinobacteria(26.66%-35.97%),Acidobacteria(17.19%-26.06%),Proteobacteria(15.07%-19.33%)and Chloroflexi(12.48%-18.59%).The difference in bacterial community composition among different conditions of control precipitation in the levels of phylum has not yet reached significant level(P > 0.05),but at the class level and the level of low abundance of bacteria has significant differences between groups in control precipitation(P < 0.05),suggesting that the desert grassland advantage soil bacteria under the condition of rainfall has stability,plays an important role in the stability of the soil ecological function to maintain.A total of 21 bacterial groups were found to have significant differences among different conditions of control precipitation(LDA=3.0).With the increase of precipitation,the number of bacterial groups with significant differences increased,and the resource-limited and drought-tolerant response patterns were mainly displayed among conditions of control precipitation,which could be used as an indicator groups for the change of bacterial community structure under precipitation changes.Add precipitation and decreasing precipitation treatments reduced the numbers of significant interaction between bacteria,the numbers of positive correlation under reducing precipitation treatments was higher than the numbers of negative correlation,and the number of negative correlation under increase precipitation treatments was higher than the positive correlation,showed that precipitation change will change the interactions between species,reduce precipitation is advantageous to the cooperation between the species,increased precipitation is conducive to competition among species.(3)The ?-diversity of bacteria was significantly different among different conditions of control precipitation,and the bacteria richness(ACE)index under 20%precipitation increasing gradient was significantly higher than that under 40%precipitation decreasing gradient(P<0.05).The Shannon-Wiener index of bacteria under precipitation adding treatments was significantly higher than that of the control group,while the Simpson index was significantly decreased under precipitation adding gradient(P<0.05).However,there was no significant difference in the bacterial?-diversity among different precipitation gradients,indicating that the effect of precipitation change on the ?-diversity of soil bacterial community was more obvious than that of ?-diversity in desert grassland region.(4)The main plant and soil factors that affected bacterial community composition were plant richness,plant density,plant Shannon diversity,plant coverage,SAP,EC,MBC,TN,TP and SWC(P<0.05).Among them,the dominant factors were plant richness and SAP.From the perspective of mechanism and process,control precipitation affected bacterial community composition and diversity by affecting aboveground biomass and richness of plants and comprehensive characteristics of density and coverage,respectively.