Studies On Biodiversity Of Micro-eukaryotic Plankton And Environmental Adaptation Mechanism Of The Important Groups In The North Western Pacific

Eukaryotic plankton are the most important primary and secondsry producers in the ocean,accounting for 45%of global primary production.They play important roles in regulating marine biogeochemical cycles and global climate,and they are the base in maintaining the stability of marine ecosystems.Eukaryotic plankton adjust their community structure and metabolic functions to adapt to the environmental changes when facing the complex and diverse marine environments.Recent studies on eukaryotic plankton adaptation mostly focus on in-lab cultured experiments,however,only in-field investigation can reflect the natural response of eukaryotic plankton to different environments and reveal the adaptative mechanisms of eukaryotic plankton.In this thesis,eukaryotic plankton in different regions of the northwestern Pacific Ocean were studied using a combination of high-throughput sequencing and metaproteomic approaches.The diversity,distribution of eukaryotic plankton communities in different habitats and their interaction with biotic and abiotic factors,and protein expression profiles of four key phytoplankton groups were studied.In addition,the functional differences of diatom community in different habitats were studied and the molecular mechanism involved in environmental adaptation was discussed.The main results are as follows:(1)Using the high-throughput sequencing of 18S rRNA gene,the relationship between microeukaryotic biodiversity in the northwest Pacific Ocean and biotic and abiotic factors were studied.Metazoa and Dinoflagellata were the dominant groups in the study area,and the distribution of different microeukaryotic groups were different among three regions.Environmental factors were key factors driving the distribution of microeukaryotes,while temperature was the most important environmental factor.Bacterial abundance was also an important factor affecting microeukaryotic community structure,especially for the distribution of diatoms and dinoflagellates.Moreover,distribution of different groups of eukaryotes was affected by specific bacterial groups.(2)The proteome response of four major phytoplankton groups to environmental factors were studied using metaproteomic approach.Different phytoplankton groups showed different functional expression patterns at each station,while salinity and NH4+were key factors driving the expression of phytoplankton proteins.Translation,signal transduction and folding,sorting and degradation of metabolic pathways were important processes for phytoplankton adaptation to environments.Expressions of metabolic functions of the four major phytoplankton groups at each station were significantly different,as well as expressions of environment adaption proteins.Furthermore,the relationship between them and environmental factors were also significant different.(3)The diatom community in three habitats was dominanted by different diatom groups.The relative abundance of diatoms in coastal waters is much higher than that in open ocean,which were domained by Corethron and Actinocyclus,however,Pseudonitzschia and Chaetoceros dominated the open ocean.The function analysis of differentially expressed proteins indicated that diatoms showed different adaptative mechanisms between the coastal waters and the open ocean,especially in the open ocean,the mechanism was also different due to different environmental characters.However,diatoms maintained high expressions of transcription and nucleic acid metabolism in order to maintain the potential for rapid growth to and reproduction when facing appropriate environment conditions.In general,this thesis systematically studied the eukaryotic plankton community structure and environmental driving factors in the northwest Pacific Ocean using highthroughput sequencing and metaproteomic approach.The protein expression profiles were analyzed and environmental adaptation mechanisms and strategies of key phytoplankton groups were revealed.This thesis improves our understanding of the diversity and environmental adaptability of eukaryotic plankton in the northwestern Pacific Ocean and provides a data base and scientific basis for further study of eukaryotic plankton in the northwest Pacific Ocean in the future.