Influence of Pioneer Phytoremediation-induced Rhizosphere Microdomains on the Morphological Differentiation of Heavy Metals in Lead-Zinc Smelting Slag

In order to study the effect of typical pioneer herb plants in the metal smelting slag dump on the nutrients and heavy metal forms of the slag, the pioneer herb (Trifolium repens, Lolium perenne) rhizosphere microdomains on the lead-zinc smelting slag dump that has carried out vegetation reconstruction for 5 years were used as the research object, analyzing the differentiation characteristics of heavy metal content, occurrence forms and nutrients in two kinds of herbaceous plant rhizosphere micro-domain waste residues with different particle sizes (<0.25, 0.25~0.5, 0.5~1, 1~2, 2~5, >5 mm) during the ecological restoration process. The results showed that the plant nutrients in the waste residue were mainly distributed in the small particle size waste residue <1 mm; the organic matter and total nitrogen content in the plant rhizosphere and non-rhizosphere waste residues generally increased first and then decreased with the increase in the size of the waste residue. The content of available nitrogen and available phosphorus decreased with the increase of the particle size of the waste residue; the improvement effect of the two herbaceous plants on the nutrients of the waste residue was mainly expressed as clover> ryegrass> control, and showed obvious rhizosphere effects (rhizosphere> non rhizosphere). Two phytoremediation effects significantly affect the heavy metal content of waste residues and the distribution of their occurrence forms in different particle sizes: (1) The content of Pb and Cu in clover rhizosphere waste residue was significantly lower than that of the control, and promoted the conversion of Cd to residue; (2) The content of Cu and Cd in ryegrass rhizosphere waste residues with different particle sizes is redistributed, and the content in the fine particle size (<0.5 mm) waste residues is significantly reduced; (3) The ratio of acid soluble Cu, Pb, Cd, and Zn of the two plant rhizosphere waste residues decreased significantly, and the ratio increased with the increase of the waste residue particle size. In conclusion, trifoliumrepens and loliumperenn as pioneer plants in ecological rehabilitation of waste slag yards, can create good planting conditions for the natural settlement of dominant plants, and are of great significance to the control of the ecological risk of the diffusion and migration of fine-sized waste slag.