Primary Succession Changes the Composition and Functioning of the Protist Community on Mine Tailings, Especially Phototrophic Protists

Primary succession
in mine tailings is a prerequisite for tailing
vegetation. Microorganisms, including bacteria, fungi, and protists,
play an important role in this process in the driving force for improving
the nutritional status. Compared to bacteria and fungi, protist populations
have rarely been investigated regarding their role in mine tailings,
especially for those inhabiting tailings associated with primary succession.
Protists are the primary consumers of fungi and bacteria, and their
predatory actions promote the release of nutrients immobilized in
the microbial biomass, as well as the uptake and turnover of nutrients,
affecting the functions of the wider ecosystems. In this study, three
different types of mine tailings associated with three 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. The keystone phototrophs of Chlorophyceae
and Trebouxiophyceae showed the highest relative abundance in the
biological crusts and grassland rhizosphere, respectively. In addition,
the co-occurrences between protist and bacterial taxa demonstrated
that the proportion of protistan phototrophs gradually increased during
primary succession. Further, the metagenomic analysis of protistan
metabolic potential showed that abundances of many functional genes
associated with photosynthesis increased during the primary succession
of tailings. Overall, these results suggest that the 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. This research offers an initial insight into the changes
in biodiversity, structure, and function of the protistan community
during ecological succession on tailings.