Study On Protozoa Community In The Land Water Ecotone Of Harbin Based On High-throughput Sequencing

The land and water ecotone serves as a crucial crossroads between ecosystems on water and land.There is an urgent to strengthen management and ecological monitoring in this area.The protozoa community is a crucial component of the ecotone ecosystem and plays an important role in the microbial food web,material cycle and energy flow of the ecosystem.Its community structure is strongly related to environmental factors,and it has an indicative role in environmental changes.However,there are still many deficiencies in the understanding of the mechanism and driving factors of protozoa community construction,especially the studies on the protozoa community in the land and water ecotone zone need to be supplemented.In this study,36 sediment samples were collected in May（normal season）,July（wet season）and October（dry season）from four sampling points in Songhua River of Harbin section,and 14 physical and chemical indicators of each sample were measured.18S rDNA high-throughput sequencing technology was used to study the protozoa community composition,diversity,distribution characteristics and the relationship between protozoa and specific environmental factors.The main results are as follows:1.A total of 2,584,382 sequences and 10,631 ASVs were obtained,4,860 ASVs protozoa ASVs were identified.Ciliophora,Cercozoa,Evosea and Tubulinea are the dominant groups at the phylum level.Heteromita,Sorodiplophrys,Schizoplasmodium,Frontonia,Bicosoeca,Gymnophrys,Cercomonas,Vermamoeba,Rhogostoma,Cryptocaryon,Colpodella,Lecythium,Tintinnidium and Flamella are dominant groups at the genus level.2.The results of Alpha diversity analysis showed that the diversity of protozoa community was in the order of wet season>dry season>normal season;Zhu Shuntun>Songbei District>Hulan Estuary>Dadingzi Mountain.Affected by Harbin city,the Chao1 index has significant differences among sample points.3.The seasonal differences of protozoa communities were analyzed.The results showed that at the phylum level,the relative abundance of Apicomplexa,Cercozoa,Evosea,Heterolobosea and Tubulinea varied significantly among the three seasons.There are 15 taxa at genus level difference,respectively:Tintinnidium,Vermamoeba,Platyophrya,Rhogostoma,Sorodiplophrys,Lecythium,Schizoplasmodium,Cercomonas,Flamella,Heteromita,Phalansterium,Prorodon,Blepharisma,Bicosoeca and Colpodella。The analysis of neutral community model shows that the deterministic process dominates the establishment of protozoa community.Mantel test showed that WT was the main factor driving the seasonal variation of protozoa diversity.Spearman correlation analysis showed correlation factors were SWC,pH,TP and SOM.BIOENV analysis showed that pH and TP were the main environmental factor combination.4.The spatial heterogeneity of protozoa communities was analyzed.The results showed that the relative abundance of Ciliophora,Discosea,Cercozoa,Evosea,Tubulinea,Preaxostyla and Perkinsozoa was significantly different among the four sites at the phylum level.There are 26 taxa with genus level difference,respectively:Aspidusca,Bicosoeca,Bryometopus,Blepharisma,Cercomonas,Cyphoderia,Colpodella,Colpoda,Dileptus,Gymnophrys,Frontonia,Heteromita,Ischnamoeba,Lecythium,Obertrumia,Phalansterium,Prorodon,Pseudoplatyophrya,Pseudouroleptus,Pseudochilodonopsis,Rhogostoma,Stokesia,Sorodiplophrys,Schizoplasmodium,Tintinnidium and Zosterodasys.The analysis of neutral community model showed that the establishment of protozoa community was determined by deterministic process.The community of Dadingzi Mountain was influenced by diffusion limitation.Mantel test showed that SWC,TK and NO₃^--N were the main factors driving the spatial variation of protozoa diversity.Spearman correlation analysis showed that pH,WT,NO₃^--N and TK were the correlation factors.BIOENV analysis showed that WT,pH,TK and NO₃^--N were the main environmental factor combination.