Study On The Phytoplankton Spatial-temporal Distribution And Co-occurrence Network In The Bohai Bay Using RbcL Gene Technique

Bohai Bay is a typical semi-enclosed shallow water bay with gentle slope silt,and its self-purification ability is very poor.In recent years,Bohai bay ecological environment problems have obvious influence and restrict the sustainable development of bohai rim regional economy and Marine the recycling of material resources.Phytoplankton plays an important role in maintaining the dynamic balance of the marine ecosystem.When the marine environment changes,the phytoplankton community structure will change rapidly,so it is usually used as an indicator of marine ecological environment changes.This paper comprehensively studied the changes of phytoplankton community structure and its influencing factors in different time and space in Bohai Bay in 2020,which indirectly indicated the Marine ecological environment in different periods and provided theoretical basis for ecological restoration.This research use the rbcL gene study of phytoplankton has high resolution for summer and autumn the phytoplankton community composition and diversity of the surface waters of the bohai bay and the correlation with environmental factors,and making use of the qPCR quantitative diatoms and whip algae are two main phytoplankton rbcL gene,to verify the accuracy of high-throughput sequencing results.Meanwhile,the phytoplankton co-occurrence network and phytoplankton-bacteria co-occurrence network were constructed based on SparCC method,and the stability of the co-occurrence network in summer and autumn was analyzed according to the topological properties of the network.The results showed that the abundance distribution of rbcL gene in diatoms and Haptophytes was basically the same as that of the OTUs.In terms of community composition,the genus Teleaulax dominated in summer,followed by Chrysochromulina.Thalassiosira,Paralia and Dictyocha.The abundance of phytoplankton in autumn was the highest in Paralia,followed by Nannochloropsis and Chrysochromulina.In addition,rbcL gene also identified more phytoplankton species,which added new content to phytoplankton composition in Bohai Bay.The diversity analysis showed that the phytoplankton diversity was different in summer and autumn,and the difference was more significant in autumn(P<0.05).NMDS analysis based on diversity showed the same clustering results as PAM analysis based on environmental factors,so the spatial and temporal distribution of phytoplankton was regulated by environmental factors.RDA analysis showed that salinity,dissolved oxygen and pH were the main environmental factors affecting phytoplankton community in summer,while temperature and nutrients were more significant in autumn,in addition,residual currents also play an important role in shaping the spatial distribution of phytoplankton.The importance ranking based on random forest showed that dissolved oxygen,COD and inorganic nitrogen were the main environmental factors affecting the seasonal variation of phytoplankton distribution in time distribution.In summer and autumn,the co-occurrence patterns of the phytoplankton networks were diatom-diatom and diatom-Haptophytes,but the key species were different in summer and autumn.The negative correlation mainly occurred between modules,indicating that phytoplankton competition in the environment was not pure interspecific competition,but competition among different co-occurring phytoplankton communities.Pearson correlation analysis between phytoplankton co-occurrence network module and environmental factors showed that the environmental factors driving the formation of phytoplankton co-occurrence network module were very different in summer and autumn.In summer,the main factors were pH,dissolved oxygen,nutrient salts and their proportion,while in autumn,the main factors were temperature,salinity,dissolved oxygen and COD.The phytoplankton-bacteria interaction network based on 16S rDNA and rbcL genes showed that the interaction between proteobacteria and phytoplankton dominated the phytoplankton co-occurrence network in summer and autumn.Proteobacteria and phytoplankton had a high degree of connectivity in the network in summer and autumn,but the bacteria with which they interacted were different.Mantel test showed that the seasonal variation of environmental factors such as temperature,pH,dissolved oxygen,COD and NO3-N affected the phytoplankton-bacteria co-occurrence pattern in summer and autumn.Combined with the eutrophication assessment results of environmental factors,phytoplankton diversity,and the comparison of topological properties of the two co-occurrence networks in summer and autumn,the eutrophication degree was higher in summer,and the proportion of negative correlation between the two networks was larger in autumn,and the ecological environment was more stable in autumn than in summer.