Spatial Distribution And Diversity Analysis Of Microbial Eukaryotes Under The Influence Of Qiongdong Upwelling

Upwelling plays an important role in marine ecosystems and potentially reshapes microbial communities by enhanced dispersal and distinct environmental drivers.However,compared with bacterioplankton and zooplankton,the response of eukaryotes to the influence of upwelling is largely unknown.In this study,the difference of abundance between microbial eukaryotes and bacterioplankton in Qiongdong upwelling area were compared.The influence of upwelling on the community structure of microbial eukaryotes was explored by using molecular biology techniques and ecological analysis methods.The results are listed as follows:Microbial eukaryotes and bacterioplankton showed different response modes to upwelling.Upwelling promoted the growth of bacterioplankton significantly,which increased the abundance of bacterioplankton in surface water by nearly 5 times,with the highest abundance of 2.93×10~6 cells/m L,and the abundance of bacterioplankton decreased rapidly with the increase of depth.However,upwelling had little effect on the abundance of microbial eukaryotes.In the coastal upwelling region,the abundance of microbial eukaryotes increased slightly with the increase of depth,with the maximum value(12.53×10~4 copies/m L)in non-upwelling deep water.In the offshore region,i.e.,non-upwelling region,the abundance of microbial eukaryotes and bacterioplankton changed little with depth,and both have maximum value in the middle layer.The results of community diversity analysis of microbial eukaryotes showed that the upwelling increased the relative abundance of 100 dominant ASVs(amplicon sequence variants)in surface water with the percentage up to 65.47%,and significantly reduced the evenness of microbial eukaryotic community,which may be the embodiment of upwelling’s"selectivity effect".Compared with microbial eukaryotes,the upwelling enhanced theαdiversity of bacterioplankton.There were no significant correlations between theαdiversity index of microbial eukaryotes and any environmental factors,but the Shannon diversity index of bacterioplankton and the number of ASV were positively correlated with depth,and the number of ASV was negatively correlated with temperature.There were significant differences in the composition of microbial eukaryotic communities in different habitats,especially in the upwelling surface and non-upwelling surface areas.In the upwelling surface water,the relative abundances of eukaryotic microbiomes in Sagenista and Bacillariophyta of the Stramenopiles supergroup were higher.The microbiomes in the Dinoflagellata of the Alveolata supergroup occupy a dominant position in the non-upwelling surface,while the growth of Dinoflagellata is inhibited in the upwelling area.No matter in the upwelling area or the non-upwelling area,the microorganisms in Radiolaria were dominant in deep water.Temperature was the most important environmental factor to shape the structure of microbial eukaryotic community,which indicates the potential influence of cold-upwelling water mass on microbial eukaryotic communities.Generally speaking,the results of this study revealed the different responses of microbial eukaryotes and bacterioplankton to coastal upwelling,and explored the remarkable and unique impact of coastal upwelling on microbial eukaryotic biodiversity and community structure,filling the knowledge gap of response mode of eukaryotes to this important marine phenomenon and providing scientific basis for further exploring the ecological function of upwelling and the important role of microbial eukaryotes in upwelling.