Abstract:

In order to optimize the application of plant-assisted bioremedation to mining wasteland, the Dabaoshan mining wasteland in Shaoguan, Guangdong Province was investigated through in situ remediation field experiment to assess the effects of different treatment plans—consisting of companion planting (trees, shrubs, grass crops) and soil conditioner application—on heavy metals (HMs) and microorganisms in mining wasteland. The bioconcentration factor (BCF), biotransfer factor (BTF) and HM retention rate were calculated and compared for the dominant plants to assess their HM remediation capacity. Based on the results of high-throughput soil DNA sequencing, the relationship between soil microbiome richness and diversity and environmental factors was discussed. Five dominant plants were identified under different treatment plans and showed varying remediation capacities. In the dominant plants, the overall BCF and BTF of heavy metals followed the order of Cd > Cu > Zn > Pb, and HM retention rates were Pb > Zn > Cu > Cd. Heavy metal contents in roots, stems and leaves of different plants varied greatly. Among the five dominant plants, Cd concentrated most in the stems and leaves of Pinus elliottii and Lagerstroemia indica, and HMs accumulated in roots of Plantago asiatica and Ligustrun lucidum Ait.; while Boehmeria nivea was resistant to HMs via avoidance. All treatment plans significantly reduced Cd/Pb soil contents by more than 50%. The addition of soil conditioners and use of companion planting significantly increased soil microbiome richness and diversity, where plan D showed the largest reduction of Cd bioavailability and plan C the highest microbiome diversity. Proteus and Actinomycetes were the dominant flora in all soil samples. Furthermore, companion planting of high tolerance plants significantly reduced Cd/Pb bioavailability, altered soil microbiota profile, and helped to increase the abundance of HM resistance flora and establish a healthy soil microbiota, thereby achieving effective bioremediation of mining wasteland. Companion planting of high tolerance trees, shrubs and grasses with variable plant combinations is the best phytoremediation strategy for mining wasteland.

Key words: ecological restoration, mining wasteland, heavy metals pollution, soil microorganisms, community structure