Mechanism of Lead-zinc Enrichment and Resistance of Spent Mushroom Compost to Lead-Zinc Slag in Koelreuteria paniculata

Abstract

Phytoremediation is an ecological technique for tailing area restoration; adding substrate modifiers can reduce the stress of heavy metals on plants and enhance the restoration efficiency. The woody plant Koelreuteria paniculata was used as a test plant and potted in 100% tailings (S), 90% tailings+5% mushroom residue (SMC)+5% CaCO3 (MS), and natural red soil (RS). The effects of physiological responses and tolerance enrichment effects on Pb and Zn tolerance in K. paniculata under different treatments were investigated to compare the growth morphology, microscopic morphological changes, and microbial diversity changes in each substrate of K. paniculata seedlings. The results showed that compared with the control group S, the MS treatment group could significantly improve the structure and fertility of the tailing substrates; significantly enhance the relevant physiological indicators such as biomass, plant height, and chlorophyll content of K. paniculate; and increase the accumulated heavy metal content in K. paniculata. In the treatment group, the overall physiological indexes of MS compared to RS biomass and plant height were promoted, and the total root length increased up to 69.3%, whereas the average root diameter of RS in the treatment group decreased 118.7% compared to that in the control group S. The MS treatment group showed a 266.67% increase in Pb and Zn residue state, a significant decrease in the weak acid extractable state and oxide-bound state compared to that in the control group S. The heavy metals were less active for plant migration. Furthermore, most of the heavy metals were trapped in the roots of K. paniculata, and the changes in its root conformation indicated its strong adaptability in the face of high Pb stress. Transmission electron microscopy (TEM) analysis showed that the higher concentration of heavy metals in the S control damaged the cell wall structure and caused toxic effects on plant cells. The addition of the modifier effectively alleviated the effects of heavy metal stress on various tissues of K. paniculata, affected the structure of microbial communities, significantly increased microbial richness and diversity, and enhanced the adaptability of K. paniculata to heavy metals and phytoremediation ability.