| Protozoa are a large group of unicellular animals that play a crucial role in biogeochemical cycles and aquatic micro food webs,and they are sensitive to environmental changes,so they are often used as indicator organisms to reflect changes in the aquatic environment.With the development of high-throughput sequencing technology,the protozoan diversity and spatial and temporal distribution characteristics of many research hotspots have been reported one after another,but the study of protozoan diversity and its biogeographic patterns in hot springs/thermal springs in southern Tibet is still rarely addressed.In order to investigate the diversity,spatial and temporal distribution characteristics,community influencing factors and the relationship between protozoan communities and aquatic environmental factors in hot springs/thermal springs in southern Tibet,a total of 132 DNA samples were collected from 44 sample sites in hot springs/thermal springs in southern Tibet in June,August and October 2020,respectively.Based on the18 s rDNA method,the DNA samples were sequenced by high-throughput sequencing,and the sequencing data were analyzed by bioinformatic analysis to explore the alpha diversity of protozoan communities,analyze the community characteristics of protozoan communities in different hot spring types and their influencing factors,and analyze the topology of community cooccurrence network and the relationship between protozoan diversity and aquatic environmental factors in different hot spring types.We also evaluated the water quality using protozoan diversity.The main conclusions are as follows:(1)Based on 18 s rDNA sequencing,a total of 1750 protozoan ASVs were obtained from hot springs/thermal springs in southern Tibet,and a total of 198 species of 187 genera in 11 phyla and 52 orders and 70 families of protozoa were identified.Among them,Phylum Ciliophora,Phylum Filipoda and Phylum Amoebae accounted for the most,and the rest,such as Phylum Ophidia,Phylum Filipoda,Phylum Polychaeta and Phylum Amoebae communities accounted for less,but the distribution was visible in all kinds of sites.(2)The α-diversity indices of hot springs/thermal springs protozoa in southern Tibet did not differ significantly among hot springs types,and the values of Shannon diversity index,Simpson diversity index and Pielou evenness were higher for thermal springs than for micro/low temperature springs than for hot springs.the Richness index was higher for micro/low temperature springs than for thermal springs than for hot springs.(3)Multicollective Venn diagrams showed that a total of 1750 ASVs were obtained in hot springs/thermal springs in southern Tibet,with a total of 148 ASVs of all species in all hot spring sample sites,and different hot spring types had their componentspecific protozoa.Among them,853 ASVs were present in micro/low temperature hot springs,267 ASVs were present in hot springs,and 158 ASVs were only present in hot springs.Among the different hot spring/thermal spring types in southern Tibet,the micro/low temperature hot spring habitats had the most protozoan species,followed by hot springs and thermal springs.(4)There were significant differences in β-diversity of hot springs/thermal springs protozoa in southern Tibet.β-diversity was decomposed into components according to the pattern of species turnover and species nesting,and the results showed that the differences in β-diversity were mainly dominated by the turnover component.(5)Principal coordinate analysis(PCo A)and similarity analysis(ANOSIM)based on Bray-Curtis distance was conducted on the protozoa of different hot springs/thermal springs in southern Tibet,and the results showed that the protozoan communities were grouped among different hot spring types,and the protozoan communities of different hot spring types differed in species composition and species abundance.The differences in species composition and species abundance among different spa types were not significant.Spearman’s correlation regression analysis between protozoan community similarity and geographic distance showed that the decay of community similarity in geographic distance indicated that the protozoan community variability in hot springs/thermal springs in southern Tibet was influenced by geographic distance,and the spatial distribution characteristics of protozoan communities were consistent with the general pattern of biogeographic distribution.(6)The distribution of the major taxa of the hot spring/thermal spring protozoan community in southern Tibet was significantly influenced by chemotactic factors,and the distribution constraints of each major taxa were different.Parabasalia was significantly and positively correlated with p H,and Phylum Dermatophagus was significantly and positively correlated with DO and BOD.The RDA analysis of protozoan community composition and physicochemical factors showed that,among all environmental factors,water temperature had the most significant effect on the distribution of major taxa in the protozoan communities of hot springs/thermal springs in southern Tibet.The results of RDA analysis of protozoan community diversity indices and physicochemical factors obtained that water temperature and p H had the greatest influence on protozoan diversity.(7)The results of the cooccurrence network analysis of the protozoa of hot springs/thermal springs in southern Tibet showed that among the different hot spring types,the cooccurrence network of the protozoa in micro/low-temperature hot springs was more complex,and the linkages among the taxa in the cooccurrence network were closer,and the community structure of the cooccurrence network was more stable,while the cooccurrence networks of the protozoa of hot springs and thermal springs were looser and the community structure was simpler.This indicates that the micro/low temperature hot spring protozoan communities are more resistant to disturbance than the hot spring and thermal spring types.(8)The biological evaluation of water quality shows that most of the sample sites of hot springs/thermal springs in southern Tibet are the cleanest and cleanest water bodies with good water quality conditions and no pollution. |
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