| Protozoa are single-celled eukaryotic microorganisms with morphological and genetic diversity,and as single-celled organisms,they multiply rapidly and can serve as a source of nutrition for other aquatic animals.At the same time,protozoa play an important role in the material circulation and energy flow of benthic ecosystems.Basic research on protozoa provides important materials for exploring the origin and evolution of eukaryotes and plays an important role in maintaining the stability of thermal springs/hot springs ecosystems.Exploring the diversity of protozoa communities,community construction factors and ecological processes in the extreme environment of hot springs and hot springs in southern Tibet is conducive to deepening the understanding of biodiversity,ecological functions and evolutionary information.In this study,we used 18 S r DNA gene sequencing,combined with multivariate ecological and statistical methods to analyze the distribution and community assemblage of protofauna in an extreme ecosystem such as thermal springs/hot springs in southern Tibet.In determining the main factors affecting protozoa community construction,we used co-occurrence network analysis and zero model construction to explore the effects of three factors,namely environmental factors,spatial factors and species interactions,on protozoa communities in surface sediments of thermal springs/hot springs in southern Tibet,and explored the intrinsic effects of different gradients of environmental factors and different thermal springs/hot springs surface sediment types on protozoa community construction,comparing the effects of species interactions between protozoa and algal communities on protozoa communities.The main study findings were as follows.(1)A total of 8,513,086 high-quality sequences were obtained from41 thermal springs/hot springs samples from southern Tibet,which were classified into 3,292 ASVs and identified as belonging to eukaryotes.Among the eukaryotes,there were 816 ASVs in protozoa,distributed in 10phyla;422 ASVs in algae,distributed in 7 phyla;and 2054 ASVs in other classes.When the annotated ASVs were analyzed at the phylum taxonomic level,there were 7 dominant phyla in the protozoa community,and each species had different proportions of Ciliophora(Ciliophora)and Filopodia(Cercozoa)were distributed at each site.(2)The protozoa and algal community structure is driven by a combination of environmental,spatial and species interactions.Elevation,temperature,salinity,conductivity,and p H were significant explanatory variables for the protozoa communities of thermal springs/hot springs in southern Tibet.(3)By comparing the differences in community composition of surface sediment protozoa at different elevations,p H and temperature gradients,the results showed that protozoa of the phylum Amoeba and Ciliophora lived predominantly between hot springs at 30°C-45°C under different temperature gradients.At different p H gradients,both p H 6-7(acidic hot springs)and p H 7-8(neutral hot springs)were dominated by ciliate protozoa,and at p H 8-11(alkaline hot springs),the protozoa community structure was dominated by protozoa of the phylum Siluriformes.At different elevation gradients,it was found that the proportion of protozoa of the phylum Siluriformes gradually decreased with increasing elevation,the protozoa of the phylum Ciliophora gradually increased,and the protozoa of the phylum Amoebae were stable at different elevation gradients.(4)LEf Se analysis showed that there was a great variability in the number and species of species taxa,characteristic protozoa vary under different environmental gradients.Under the elevation gradient,the lower elevation protozoa communities were characterized by more species and showed significant differences from the middle and high elevations.By comparing the characteristic protozoa under different p H gradients,it was found that alkaline thermal springs/hot springs with higher p H had a more pronounced differential effect on the protozoa community in the surface sediments of thermal springs/hot springs in southern Tibet.Under the temperature gradient,ophidian protozoa and filamentous protozoa have special indicative roles in low-temperature environments,and ciliate protozoa have special indicative roles in high-temperature environments,and ciliate protozoa are the main taxa in high-temperature geothermal spring studies.(5)In the study of protozoa communities in surface sediments of different sediment types,the cooccurrence network of protozoa communities in sandy sediments is more complex,and the links among taxa in the cooccurrence network are closer and the structure of the cooccurrence network is more stable than that in muddy sandy sediments and muddy sediments;the cooccurrence network of protozoa communities in muddy sandy sediments and muddy sediments is looser and the results are simpler,indicating that The protozoa communities in sandy sediments are more resistant to disturbance than those in muddy sandy sediments and muddy sediments.(6)In the comparative study of protozoa and algal community building factors,the results of protozoa co-occurrence network analysis in the surface sediments of southern Tibetan hot springs indicated that the interactions between protozoa and between protozoa and algae were dominant.Protozoa communities were more susceptible to environmental factors than algal communities,and showed stronger species interactions in protozoa community species.This study is a basic mapping of the protozoa in the surface sediments of thermal springs/hot springs in southern Tibet,which can fill the gaps in related fields of research at home and abroad in extreme environments at high altitudes,and the basic study of protozoa provides important materials for exploring the origin and evolution of eukaryotes and plays an important role in maintaining the stability of thermal springs/hot springs ecosystems. |
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