Pioneer plants promote soil formation in a mixture of bauxite tailings and red mud.

The disposal of bauxite tailings and red mud is a concern for the sustainable development of the Al industry. Our previous study demonstrated that the disposal of bauxite tailings and red mud as a soil-like matrix (BRM) has great application potential for revegetation after bauxite mining with suitable pioneer species promoting soil formation in the BRM. The present study evaluated the improvement effects of six pioneer plants (Celosia argentea, Bassia scoparia, Suaeda glauca, Melilotus suaveolens, Sorghum sudanense, and Sesbania cannabina) on the physicochemical properties and microbial communities of BRM. The results indicated that the pioneer plants significantly decreased salinity and alkalinity and increased micropore volume, available phosphorus, and organic matter in the BRM (p < 0.05). Furthermore, microbial diversity and network stability in BRM significantly increased after planting pioneer plants. The partial least-squares path model analysis showed that pore structure improvement was most important in the plant promotion of soil formation in BRM. Although all six plants grew well on BRM, C. argentea had the highest shoot biomass and root volume. Compared with other plants, C. argentea increased the micropore volume of BRM. In addition, M. suaveolens showed a greater ability to regulate BRM salinity and alkalinity, resulting in a more significant decrease in the abundance of halophilic bacteria. A comprehensive evaluation based on gray relation analysis indicated that C. argentea and M. suaveolens are suitable pioneer plants for revegetation in BRM disposal areas.