[Effects of Reservoir Water Depth on Different Plankton Communities and Keystone Species of Network Interaction]

In order to understand the impacts of the reservoir construction on the diversity and ecological network of different microbial communities, seven sampling sites were set up in the Hengshan Reservoir in 2021. Water samples were collected from the surface and bottom of the reservoir. After filtering and extracting total DNA samples, high-throughput sequencing was carried out based on 16S and 18S rDNA to investigate the response of community structure, molecular ecological network, and keystone species of different microbial groups to water environment changes. The results showed that the Richness, Simpson, Shannon, and Pielou's Evenness indices of bacterial community in the surface and bottom layers were higher than those in the eukaryote community. The dominant community of bacteria included Proteobacteria, Actinobacteria, and Bacteroidetes, and the eukaryote community included Arthropoda, Ciliophora, Ochrophyta, etc. Moreover, the density and average clustering coefficient of the microbial networks in the surface waters of different phytoplankton communities were higher than those in the bottom waters. It was also observed that the microbial ecological networks in the surface waters were more closely related, and the number of nodes and edges, as well as the number of keystone species, of bacterial communities in the surface and bottom layers were significantly higher than those in the eukaryote microbial communities, indicating that the bacterial community network was larger, and the cooperative relationship and network connectivity between species were stronger. The interaction between bacterial community and eukaryote community in different water depths was dominated by positive correlation, and the negative correlation of the two groups in the bottom layer was slightly greater than that in the surface, indicating that the competition between bottom-layer species was greater than that between surface-layer species. In addition, the environmental impact factors of all species and keystone species of the community in surface water were basically the same, but they differed greatly in deep water, indicating that the influence mechanism of water depth change on keystone species was not the same as that of all species. The results further revealed the effects of reservoir construction on the stability and interspecific interactions of different microbial communities and provided a theoretical basis for predicting variations in microbial community and material cycling in reservoirs.

[Diversity of Soil Eukaryotic Microbes in Different Succession Stages in Maolan Karst Forest of Guizhou]

As an indispensable part of the Maolan karst forest soil microorganisms, eukaryotic microbes play an important role in ecosystem material and energy flow. To investigate the composition and diversity of soil eukaryotic microbial communities under different succession stages in the Maolan karst forest, we explored the diversity and composition of soil eukaryotic microbes under four succession stages of primary forests (YSL), shrub forests (GML), bushes (GMC), and grassland (CD) via high-throughput sequencing (HTS) of the 18S rDNA. The results showed that the composition of soil eukaryotic microbial communities was similar in different succession stages under different classification levels. There was a significant difference in α diversity, Shannon, and Simpson's indices at different stages of succession as follows: YSL > GMC > GML > CD. The non-metric multidimensional scaling analysis showed that there were differences in the soil eukaryotic microbial community structure at different succession stages. The linear discriminant analysis effect size (LEfSe) analysis showed that the number of differential indicator species in YSL was higher than in GML, GML, and CD. The results of our study provide a theoretical basis for further research on soil eukaryotic microorganisms in different succession stages.

Species delimitation for the molecular taxonomy and ecology of the widely distributed microbial eukaryote genus Euplotes (Alveolata, Ciliophora)

Recent advances in high-throughput sequencing and metabarcoding technologies are revolutionizing our understanding of the diversity and ecology of microbial eukaryotes (protists). The interpretation of protist diversity and the elucidation of their ecosystem function are, however, impeded by problems with species delimitation, especially as it applies to molecular taxonomy. Here, using the ciliate Euplotes as an example, we describe approaches for species delimitation based on integrative taxonomy by using evolutionary and ecological perspectives and selecting the most appropriate metabarcoding gene markers as proxies for species units. Our analyses show that: Euplotes (sensu lato) comprises six distinct clades, mainly as result of ecological speciation; the validity of the genera Euplotes (sensu stricto), Euplotoides, Euplotopsis and Moneuplotes are not supported; the vannus-type group, which includes species without distinct morphological differences, seems to be undergoing incipient speciation and contains cryptic species; the hypervariable V4 region of the small subunit rDNA and D1-D2 region of the large subunit rDNA are the promising candidates for general species delimitation in Euplotes.