Effects Of Nitrogen And Phosphorus Addition On Rhizosphere Soil Bacterial Community Of Three Typical Halophytes In The Yellow River Delta

Due to the influence of human activities,the nitrogen（N）input to terrestrial ecosystems has been increasing continuously.The Yellow River Delta has become the region with relatively high N deposition in China.Compared with N input,phosphorus（P）input increased less,which seriously changed the N and P input ratio of natural ecosystems and hindered the process of nutrient cycling,which in turn may cause changes in the structure and function of ecosystems.Soil microbes are the engines of nutrient cycling,regulating the ecosystem response to human-induced increases in N and P effectiveness.Therefore,studying the response of soil microorganisms in the Yellow River Delta to changing nutrient input conditions is essential to predict the future impact of increased N and P inputs on the ecosystem.In this work,four N addition treatments(N0:0 kg N ha^-1,N1:50 kg N ha^-1,N2:150 kg N ha^-1,N3:450 kg N ha^-1)and two P addition treatments(P0:0 kg N ha^-1,P1:100 kg N ha^-1)were set up to study the bacterial communities of three different types of halophytes in the Yellow River Delta.Using control experiments,soil measurement and 16s r RNA sequencing to investigate the effects of N and P addition on the bacterial communities of rhizosphere and bulk soils of halophytes.The bacterial communityα-diversity,β-diversity,structural composition was analyzed to explore the effects of plants on soil bacterial communities in the background of N and P addition,to reveal the effects of different rhizosphere soil bacterial communities of halophytes on N and P addition,to investigate the effect of plant on soil bacterial communities in the background of N and P addition and to reveal the differences in the response of soil bacterial communities to N and P addition and the coupling mechanism between plant-soil-bacterial communities.The main results of this work are as follows:（1）N and P addition had insignificant effect on theα-diversity of rhizosphere soil bacterial communities in Suaeda salsa and a significant effect on that of bulk soil bacterial communities.The bacterial communityα-diversity of the rhizosphere soil was significantly higher than that of the bulk soil.High level N significantly increased the number of OTUs of bulk soil bacterial communities by 39.81%,indicating that N addition can increase the diversity of bulk soil bacterial communities.P addition increasedα-diversity under low N addition and decreasedα-diversity under high N addition,suggesting that there is a synergistic effect of P addition on bacterial diversity of bulk soils at low N level addition.N and P addition had significant effects on the bacterial community structure of rhizosphere and bulk soils,and the effects on the bacterial community of rhizosphere soils were higher than that of bulk soils.In bulk soils,N and P addition increased the relative abundance of the Bacteroidetes and decreased that of Acidobacteria and Actinomycetes.The relative abundance of the Bacteroidetes and Actinomycetes was higher and lower in rhizosphere soils than in bulk soils,respectively.The Shannon index of bulk soil bacterial communities was significantly and positively correlated with total carbon（TC）,total phosphorus（TP）,total nitrogen（TN）,available phosphorus（AP）and soil organic matter（SOM）content,respectively.The SOM content had the greatest effect on bacterial community structure,and p H had the greatest effect on the dominant phylum and genus composition of the bacterial community.（2）There were insignificant effects of N addition on OTUs in the rhizosphere bacterial community of Aeluropus sinensis.N and P co-addition increased the OTUs and Chao1 index by 14.03%compared to the control treatment.P addition increased the Shannon index of the bacterial community at the same N addition level.P addition significantly changed the rhizosphere soil bacterial community structure,while there was no significant effect on the bulk soil bacterial community structure.The Bacteroidetes and Gemmatimonadetes in bulk soils increased with N addition level.The N3P1 treatment significantly decreased the relative abundance of Chloroflexi,Bacteroidetes,Verrucomicrobia and Actinomycetes by 35.0%,44.8%,48.8%and 13.2%compared to the control treatment,respectively.The Shannon index of bulk soils was significantly negatively correlated with AP and p H,and significantly positively correlated with SOM content.p H had the greatest effect on bacterial community structure,phylum and genus composition.（3）Theα-diversity of bacterial communities in Phragmites australis rhizosphere soils was significantly affected by N and P additions,whileα-diversity in bulk soils was not affected by N and P addition.N3P1 treatment significantly increased OTUs,Chao1 index and Shannon index of rhizosphere soil bacterial community by 14.36%,14.00%and 3.27%compared to the control treatment.P addition significantly increased OTUs at the same N addition level.With increasing N addition level,the P addition increased OTUs in the rhizosphere soil bacterial community of Phragmites australis more significantly.N and P addition had significant effects on the bacterial community structure of both of rhizosphere and bulk soil.The relative abundance of the Firmicutes increased with increasing N addition level,reaching the maximum at N3P0 treatment.P addition increased the relative abundance of the Bacteroidetes.Chao1index was significantly and negatively correlated with SOM content.Salt and SOM content had the most significant effect on bacterial community structure,phylum and genus composition.（4）Plant species had the greatest effect on rhizosphere soil bacterial communityα-diversity and community structure among different halophytes.The interaction between plants and N and P had a significant effect on bacterial community structure,indicating that the effect of N and P addition on bacterial communities varied according to plant species.N and P addition had the greatest effect on the rhizosphere soil bacterial community structure of Phragmites australis.The rhizosphere soil of Aeluropus sinensis has more Proteobacteria.The relative abundance of Acidobacteria,Bacteroidetes and Verrucomicrobia in the rhizosphere soil of Suaeda salsa was higher than that of the other two plants.Soil salt and TC content had the greatest effect on the structure of the rhizosphere soil bacterial communities of the three halophytes,explaining 50.89%and 32.23%of the differences on the PCo A1 and PCo A2 axes,respectively.