Assessment of chemical, biochemical, and microbiological properties in an artisanal Zn-smelting waste slag site revegetated with four native woody plant species

Waste slag from artisanal Zn smelting causes serious environmental problems in China due to the dispersion of toxic metals in nearby water or agricultural ecosystems. Revegetation with native plant species stabilizes the surface of waste slag and reduces the potential risk to the ecosystem. A 4-year field investigation was conducted to examine the effect of revegetating a Zn-smelting site with four woody plant species, i.e., Robinia pseudoacacia L., Broussonetia papyrifera L., Cryptomeria fortunei L., and Arundo donax L., on the physicochemical, biochemical, and microbiological properties of the waste slag. Revegetation significantly increased the nutrient (N, P, and K) and organic matter contents, enzyme activities (invertase, neutral phosphatase, urease, and catalase), microbial biomass, and three dominant microbial (bacteria, fungi, and actinomycetes) community populations. Revegetation reduced Pb (except for R. pseudoacacia) and increased Cd (except for B. papyrifera) and Zn bioavailability in the rhizosphere of the plant species compared with the bare slag. In addition, there was an increase (in the presence of B. papyrifera and C. fortunei) or decrease (in the presence of R. pseudoacacia and A. donax) in Cu bioavailability in the plant rhizosphere. The nutrient contents were significantly positively correlated with microbial biomass and enzyme activity; however, the chemical properties (pH, EC, and available heavy metals) were poorly correlated with the biochemical and microbiological properties of the waste slag. The waste slag microenvironment was significantly improved by the four woody plant species. Furthermore, B. papyrifera exhibited the best performance with respect to enhancing the development of the micro-environmental conditions of the slag and is suitable as a native woody plant species for revegetating Zn-smelting waste slag sites.