Soil Organic Carbon Distribution And Bacterial Community Structure Of Mangrove In Sanya River

Mangrove is a kind of unique forest ecosystem growing in the coastal wetland intertidal zone,which is characterized by high productivity and stable structure.It plays an important role in windbreak and sand fixation,water purification,coastal protection,biodiversity maintenance,and promoting coastal material circulation and energy flow.Mangrove trees have a strong carbon sequestration capacity and have the highest carbon storage per unit area in the world.The characteristics of mangrove wetland,such as high humidity,high salt,strong reducibility and periodic flooding,have created its unique and rich microbial community,which plays an important role in the biogeochemical cycle of carbon,nitrogen,sulfur and phosphorus and energy flow.This paper takes the Sanya River Mangrove Nature Reserve as the research object.The soil organic carbon and environmental factors（p H,salinity,electrical conductivity,water content,particle size,total nitrogen,total phosphorus,total potassium,available phosphorus,and available phosphorus）in 100 cm deep soil were studied in different tidal zones（Sanya River tributary a segment,Linchun River b segment,Sanya River main stream c segment）and different sampling depths（surface0-20 cm,middle 20-50 cm,bottom 50-100 cm）The correlation between soil organic carbon and environmental factors was discussed.Meanwhile,high-throughput sequencing technology was used to study the characteristics of bacterial diversity,species composition and community structure in mangrove soil in the Sanya River,and the environmental factors affecting bacterial diversity and community structure were analyzed.The main conclusions were as follows:1.The variation range of soil organic carbon in high water zone a is 1.76-19.36g·kg^-1,high water zone b is 10.06-47.37 g·kg^-1,and low water zone c is 2.41-9.38g·kg^-1.At the same point with different sampling depth,the overall trend of soil organic carbon in the surface layer was larger than that in the middle and bottom layer.At the different point with same sampling depth,the difference of soil organic carbon in each reach was significant（p<0.05）,showing a trend of b>a>c.2.Spearman correlation analysis of soil organic carbon and environmental factors showed that p H（p<0.01）,salinity（p<0.05）,bulk density（p<0.01）,sand particle（p<0.01）were negatively correlated with soil organic carbon.Water content（p<0.01）,powder（p<0.01）,total nitrogen（p<0.01）,total potassium（p<0.01）,available phosphorus（p<0.01）,available potassium（p<0.01）were positively correlated with soil organic carbon;There was no obvious correlation between electrical conductivity and total phosphorus and soil organic carbon.3.On the whole,Sobs index value decreases with the increase of sampling depth,while Shannon index value decreases with the increase of sampling depth.Spearman correlation analysis results showed that salinity was significantly positively correlated with Chao index（r=0.599）and Sobs index（r=0.535）,and electrical conductivity was significantly positively correlated with Chao index（r=0.655）and Sobs index（r=0.580）.There is a significant negative correlation between available phosphorus and Chao index（r=-0.517）and Sobs index（r=-0.507）.4.Mangrove soil bacteria were abundant in Sanya River.A total of 76 phyla,235classes,619 orders,1049 families and 2221 genera were detected.At phylum level,the main bacterial groups were Chloroflexi,Proteobacteria,Actinobacteriota,Firmicutes and Acidobacteriota..At class level,the main bacterial groups were Anaerolineae,Gammaproteobacteria,Alphaproteobacteria and Dehalococcoidia.5.RDA analysis showed that 33.08%of the bacterial community was explained by environmental factors,and salinity（p=0.006）,electrical conductivity（p=0.002）,sand（p=0.021）and powder（p=0.022）were significantly correlated with bacterial community composition.The results of correlation between environmental factors and phylum level dominant bacteria showed that the relative abundance of Proteobacteria was significantly positively correlated with electrical conductivity,while the relative abundance of Actinobacteriota was significantly positively correlated with water content.The relative abundance of Firmicutes is significantly negatively correlated with electrical conductivity,and the relative abundance of Nitrospirota is significantly negatively correlated with electrical conductivity and positively correlated with available phosphorus.The mangroves in Sanya River are rich in organic carbon.This study accurately analyzed the distribution of soil organic carbon,scientifically assessed the carbon storage capacity of mangroves,and studied the correlation between soil organic carbon and environmental factors,which is of great significance for the scientific management and protection of mangrove ecosystem and the solution of global climate problems.Microbe is an important link between carbon input and carbon output and plays an important role in the carbon cycle.On the one hand,the abundance,diversity and community structure of microorganisms affect carbon sequestration and transformation;on the other hand,environmental factors can change microbial species composition and community structure,and thus affect the carbon cycle process that microorganisms participate in by influencing their respiratory metabolism and enzyme secretion.Therefore,the analysis of bacterial community structure characteristics and their relationship with environmental factors is extremely important for the study of mangrove carbon pool,and can also provide basic theoretical data for the study of microbial carbon cycle process and mechanism,which has certain reference significance.