Study On The Marine Protistan Diversity In Tropical And Subtropical Waters

Protists are main components of the marine plankton community and play a very important role in marine ecosystems:microalgae is an important source of ocean primary productivity;protozoa transfer substances and energy through microbial food webs to higher nutrient levels by feeding;particulate organic carbon is produced by the ingestion of protozoa,which will be buried in the deep sea by means of physical settlement to contribute to the biological pump;Protozoa regulate the balance of marine ecosystems by altering the composition of phytoplankton and bacteria.Therefore,protists play a very important role in the ocean,which is an important link of material circulation,energy flow and information exchange in the balance of marine ecosystems.In recent years,the development of 18S rRNA/rDNA-based high-throughput sequencing technology has enabled us to quickly obtain hundreds of thousands to millions of environmental sequences at low cost,allowing us to further study microbial community structure,evolutionary relationships and microbiological and environmental relevance.RNA provides a better representation of community composition than DNA in active protists.In the present study,we investigated protistan communities in tropical and subtropical waters by high-throughput amplicon sequencing of the V9 region of the 18S rRNA gene in order to evaluate the composition of active protistan assemblages in different environments and to understand how protistan community structure respond to environmental factors.The gaps in the study of the diversity of active protist community in tropical and subtropical waters are filled,providing a basis for future research in related fields.The main results of this study are as follows:Based on the study of the diversity of protozoan community and its response to environmental factors in the Pearl River estuary,the main results are as follows:1)The diversity of protists in the freshwater and coastal SCS stations was higher than that in the estuary,supporting Remane's artenminimum(species minimum)concept in the estuary along the salinity gradient.2)The relative sequence abundance of Stramenopiles in lower salinity stations was the highest and decreased with the increasing of salinity.However,the contributions of Alveolata,Hacrobia and Rhizaria generally increased with the increasing of salinity.3)The composition of the active protistan community was strongly correlated with salinity,indicating salinity being the dominant factor affecting protistan community composition and structure in the estuary.Through the study of the diversity of active communities and their responses to environmental factors in the South China Sea in the summer,the main results are as follows:1)The surface layer,the DCM layer(DCM,Deep Chlorophyll Maxima)and the deep community structure were significantly different.2)The protistan community of the surface are dominated by diatoms,and the DCM layer and the deep layer are mainly composed of Pelagophyceae,MAST(Marine Stramnopiles)and Ciliophora.3)Physical factors(depth,temperature and salinity)are the main factors affecting the distribution of protozoan communities in the South China Sea.4)The proportion of rich and rare species is more consistent in the samples,but their community clustering is not consistent,and the response of rare communities to environmental changes is more sensitive.On the time scale,two sizes of samples(Nano and Pico)were sampled from six sites in Xiamen,using high-throughput sequencing to study the diversity of prootistan communities and their responses to environmental factors in different months.The main results are as follows:1)There were significant differences in the diversity of protozoan communities in different months,different sites and different particle sizes.2)The interannual variability of protistan communities in Xiamen is mainly affected by temperature factors.Nano-protists are mainly dominated by Bacillariophyta in May,July and September.Pico-protists are mainly dominated by Chlorophyta in July,September and January.3)Between different months,protistan community is subject to different environmental factors.In general,the protozoan community is affected by particle size,nitrogen,phosphorus nutrient concentration,water temperature,pH,and biological factors(the abundance of viral,bacterial and Synechococcus).4)abundant species and rare species of protistan distribution patterns,there are differences in interannual variability in months scale.The full sampling of the time scale is the basis for studying the richness and diversity of rich species and rare species.The above three typical studies relate to the tropical/subtropical water in space(horizontal:estuarine/offshore,vertical:surface/DCM layer/deep),time(interannual variation in months)and particle size(Nano and Pico),which will help us to understand the diversity of active protistan community in tropical/subtropical water and to explore the response of active protistan community to environmental factors.