Primary succession changes composition and functioning of the protist community on mine tailings, especially phototrophic protists

Primary succession in mine tailings is prerequisite for tailing vegetation and microorganisms play an important role in this process. Compared to bacteria and fungi, protists populations have rarely been investigated regarding their role in mine tailings, especially for those inhabiting tailings associated with primary succession. Protists may play an important role in the primary succession of mine tailings by adjusting the food web and carbon flow. In this study, three different types of mine tailings in three different successional stages (original tailings, biological crusts, and Miscanthus sinensis grasslands) were selected to characterize the protistan community diversity, structure, and function during primary succession. Some members classified as consumers dominated the network of microbial communities in the tailings, especially in the original bare land tailings. Some keystone taxa of phototrophic protists (e.g., Chlorophyceae and Trebouxiophyceae) could be selectively enriched and became dominant in the biological crusts and grassland rhizosphere. In addition, the co-occurrences between protist and bacterial taxa demonstrated that the proportion of protistan phototrophs gradually increased during primary succession. Further, metagenomic analysis of protistan metabolic potential showed that abundances of many functional genes associated with photosynthesis incresed during the primary succession of tailings. Overall, these results suggest that primary succession of mine tailings drives the changes observed in the protistan community, and in turn, the protistan phototrophs facilitate the primary succession of tailings. Our study offers an initial insight into the changes in biodiversity, structure, and function of the protistan community during ecological succession on tailings.