Study On Hotspots And Spatial Distribution Of Denitrifying Bacterial Communities In Typical Steppe And Xilin River Wetland

Typical steppe and Xilin river wetland in Inner Mongolia are important ecological barriers in northern China and research hotspots globally.Denitrifying bacteria are important participants driving nitrogen biogeochemical cycle.Taxanomic groups and distribution hotspots of denitrifying bacterial communities are related to the source and sink transformation of greenhouse gases as well as emission reduction efficiency whereas little is known about similar studies.In this study,we constructed a reference library of denitrifying bacteria based on 16 S rRNA gene bibliometrics.Furthermore,we collected sediment/soil samples in six sample zones along the gradients from river-bed center(R1)and river-bed side(R2)zones as well as low-floodplain(W1)and up-floodplain(W2)zones in Xilin river,to Leymus chinensis(T1)and Stipa grandis(T2)zones in Typical steppe.Then we analyzed the composition,abundance,distribution and hotspots of denitrifying bacterial communities using 16 S rRNA gene and nirS gene high-throughput sequencing technology associated with bioinformatics.Meanwhile,we analyzed the response of denitrifying bacteria distribution hotspots to physicochemical factors by RDA,CCA and pearson correlation analysis.The main results of this study were as follows:(1)The reference library of denitrifying bacteria based on 16 S rRNA gene consisted of 65 genera.33 denitrifying bacterial genera from 6 samples in Typicalsteppe and Xilin river wetland subordinated to such phylogenetic branches as Proteobacteria,Actinobacteria,Firmicutes and Bacteroidetes.Among them,Proteobacteria was the largest branch.(2)16S rRNA gene and nirS gene of denitrifying bacterial communities showed a trend of increasing first and then decreasing along the R1 and R2,W1 and W2,T1 and T2 zones,and reached a peak value in low-floodplain(W1),revealing obvious spatial heterogeneity.Venn diagram showed R and W zones were dominated by shared denitrifying bacterial groups based on 16 S rRNA and nirS genes.Heatmap and principal component analysis showed that there was the highest similarity of denitrifying bacterial communities between R and W zones.(3)R1,R2,W1,W2,T2 was spatial distribution hotspots of Thiobacillus and Thauera,Hyphomicrobium and Rhodococcus,Flavobacterium and Aeromonas,Sphingomonas and Delftia,Streptomyces and Brevibacterium,respectively.Meanwhile,some denitrifying bacteria such as Bacillus and Stenotrophomonas were interlaced in R,W and T zones,showing no obvious hotspot distribution.(4)The sediment/soil of Xilin river wetland were the hotspots of Flavobacterium and Delftia,which were positively driven by water content,pH value and sand content.While the soil of Leymus chinensis and Stipa grandis steppe were the hotspots of Streptomyces and Brevibacterium,which were positively driven by organic matter,total nitrogen and total phosphorus.The results can not only make up for the lack of understanding of hotspots and spatial heterogeneity of sediment/soil denitrifying bacterial communities in Typical steppe and Xilin river wetland,but also provide scientific basis for early warning of typical steppe degradation and wetland shrinkage at different spatial scales.