Study On The Molecular Diversity,Metabolic Activity And Biogeographic Distribution Of Haptophytes (Hacrobia,Haptophyta)

Haptophytes are an important component of marine microbial eukaryotes and play a vital role in marine ecosystems as primary producers and bacterial grazers in the microbial loop.However,their vertical diversity and ecological traits still remain poorly understood.In this paper,the high-throughput sequencing with haptophyta-specific primers were used to investigate the molecular diversity and relative activity of haptophytes at vertical and horizontal scales as well as the response of different taxonomic groups to environmental parameters.The main results can be drawn as follows:1.Even dominant taxonomic groups in the environment remain a great deal of species which have not been identified yet,highlighting the extent of the unknown diversity in haptophytes.High-throughput sequencing can reveal the diversity of haptophytes in the environment to a great extent.However,the reference database for ZOTUs annotation remains to be improved with more morphological and genetic studies.2.Different clustering patterns existed between DNA and RNA samples along the water column.In DNA samples,a stratification of the communities was found with assemblages corresponding to the photic and aphotic ocean.However,in RNA samples,the mesopelagic and bathypelagic communities constituted different groups while the most similar communities were found between surface and bathypelagic zone.Bathypelagic ocean seems to be the "gene bank" which can contribute to the diversity of communities in future generations.Maximum number of unique ZOTUs and a new clade in phylogenetic tree were found in bathypelagic zone with no decrease in alpha diversity and relative activity.We speculate that the presence of haptophytes in the dark ocean may benefit from fast sinking mechanism(some cells might sink alone or within aggregates)and mixotrophic characteristics.some species with heterotrophic potential might permanently survive in the dark zone with undetermined energy metabolism.3.Prymnesiales and Prymnesiophyceae_UC were abundant groups in both surface and aphotic ocean,while Phaeocystales hosted the highest relative abundance in DCM.The different responses of taxonomic groups to environmental parameters might account for the difference.Ecologically,Prymnesiales are generally regarded as Kstrategists which might be more adapted to conditions of low nutrient on account of a mixotrophic lifestyle.While Phaeocystales might evolved as r-strategists characterized by rapid growth rates under nutrient-replete environments like DCM in the ocean.4.The community structure of haptophytes was significantly correlated with both longitude and latitude.Besides,size fractionation seemed not to separate the pico-and nano-size populations perfectly.The distribution of most taxonomic groups in different particle sizes was not significantly different probably due to the large range of cell size in the life cycle or the attachment to large particles.