Comparison of tolerance to gold tailings slag among six woody plant species under different substrate improvements

To investigate the effects of mushroom residue (SMC) addition on the improvement of gold tailings substrate and plant growth, and to screen plant species with good adaptability and tolerance to gold tailings.

In view of the problems existing in gold tailings, such as extreme nutrient deficiency, poor water and fertilizer retention capacity, unsatisfactory physical structure, excessive accumulation of heavy metals, and the dominance of herbs in existing remediation plants, Koelreuteria paniculata, Nerium oleander, Paulownia fortunei, Rhus typhina, Syringa vulgaris and Acacia podalyriifolia were selected as test plants, and mushroom residue (SMC) was used as the amendment. The physical and chemical properties of three substrates (100% gold tailings as control (CK), 90% tailings + 10% SMC (S1), 80% tailings + 20% SMC (S2)), as well as the differences in physiological and biochemical characteristics, heavy metal uptake and translocation of plants in different substrates were compared.

1) After adding SMC to tailings, the water content increased by 4.21-16.53 percentage points, total porosity increased by 12.39-25.44 percentage points, and organic matter content and cation exchange capacity increased by 66.55%-100.35% and 36.71%-63.24% respectively compared with the control.; 2) Compared with the control group, plants in the amended groups showed better overall performance in growth vigor, biomass, height increment, chlorophyll content, heavy metal uptake and translocation factor; however, there were interspecific differences among plant species within the amended groups; 3) Overall, Paulownia fortunei, Nerium oleander and Koelreuteria paniculata exhibited strong heavy metal tolerance, especially Nerium oleander, which had the best comprehensive performance under S2 treatment. The TOPSIS comprehensive evaluation method was used to comprehensively assess various physiological and biochemical indicators, and it obtained the highest score.

The addition of SMC makes the tailings structure looser and more porous, enhances water permeability and aeration, and effectively improves soil fertility. The growth and development of plants in the amended groups are generally better than those in the control group. Based on comprehensive growth and physiological indicators, Nerium oleander performs the best under S2 treatment (80% tailings + 20% SMC), and can be used as a dominant remediation plant for improved gold tailings.