Soil Bacterial Community And Functional Diversity And Greenhouse Gas Emission Patterns Under Vegetation Succession In The Yellow River Delta

Carbon dioxide（CO₂）and nitrous oxide（N₂O）are the most important greenhouse gases in the atmosphere,and soil is an important source of CO₂ and N₂O emissions.Soil CO₂ emissions mainly come from microbial respiration.Continued increases in atmospheric CO₂ and N₂O concentrations will not only cause the greenhouse effect,but even threaten the stability of global ecosystems.Soil bacteria are an important component of soil ecosystems and play an important role in decomposing organic matter and contributing to the soil material-energy cycle.Respiration by microorganisms in soil is considered to be the main source of CO₂ emissions,while N₂O production and metabolic processes involving functional genes of the nitrogen cycle are considered to be an important pathway for N₂O emissions.Therefore,studying the characteristics of soil CO₂ and N₂O emissions,changes in the abundance of nitrogen cycle functional genes,and the functional structure of soil bacterial communities and their interrelationships can help people gain insight into the diversity of microorganisms and their changes in the soil nitrogen cycle,and can provide a theoretical basis for controlling soil CO₂ and N₂O emissions.However,most studies have focused only on the single interaction between functional genes,environmental factors and greenhouse gases,and relatively little research has been conducted on the coupled interactions between the three under complex natural conditions.With the natural succession of saline vegetation,soil physicochemical properties will change accordingly,thus affecting soil bacterial communities and functions as well as the diversity of functional genes in the nitrogen cycle,which in turn affects greenhouse gas（CO₂,N₂O）emissions.In this paper,we used high-throughput sequencing to investigate the structural changes of the soil bacterial community during the succession of saline vegetation in the Yellow River Delta and to analyse the changes in the abundance of functional genes in combination with PICRUSt functional prediction.The abundance of functional genes（AOA,AOB,nir S,nir K,nos ZⅠ,nos ZⅡ,bacterial 16S r RNA）was determined and analyzed by fluorescent quantitative PCR.The main conclusions are as follows:（1）The soil bacterial resources in the study area were rich,bacterial OTU counts during vegetation succession exceeded 3,000,except in bare slate soils,and the richness and diversity of bacteria increased significantly during the succession of halophytic vegetation.Proteobacteria was the dominant bacterial phylum in the area,and it was also the dominant bacterial group that caused differences in bacterial functional structures.Stenotrophomonas is the local dominant genus,and it is also the bacterial genus that contributes the most to the differences in soil bacterial community structure during halophytic vegetation succession in the study area.（2）Soil bacteria are rich in functions.A total of 40 sub-functions are annotated in the secondary metabolic function layer,and metabolic function is the core function of soil bacteria in the study area and its relative abundance accounts for nearly 50%of Mantel analysis test showed that salinity was the key factor for the structure and functional structure of the soil bacterial community in the study area.（3）With the succession of saline vegetation,the soil CO₂ emission rate gradually increased,and the CO₂ emission rate of the soil covered with vegetation was significantly higher than that of the bare land without vegetation coverage;the soil in the study area first behaved as a sink of CO₂under the condition of flooding,and with the cultivation time Elongated,variously converted from CO₂ sinks to CO₂ sources.With the positive succession of vegetation,the N₂O emission rate gradually increased,but the cumulative emission of the moderately salt-tolerant vegetation（Aeluropus sinensis）was the largest.（4）The positive succession of halophytic vegetation has significantly increased the abundance of functional genes,The relative abundance of the six nitrogen cycle functional genes measured in this study were all in the following order:Aeluropus sinensis（Debeaux）Tzvelev.,Imperata cylindrica（L.）P.Beauv.,Artemisia capillaris Thunb.,Tamarix chinensis Lour.,Suaeda salsa（L.）Pall.,and bare land.AOB played a greater role in the nitrification process in this area,but the denitrification process was the main emission pathway of N₂O in saline soil.Notably,ammonium nitrogen,alkaline nitrogen,and salinity（conductivity）were the dominant factors leading to changes in functional gene abundance.