Abstract

--- - Purpose Mine tailings (MTs) limit plant and microbial establishment due to low fertility, poor structures, and toxic metal(loid) contents. Organic amendments (OAs) modify these conditions by increasing contents of carbon and nutrients and decreasing metal(loid) toxicity; however, the overall effectiveness of OAs remains unclear. This meta-analysis evaluated the effects of OAs on the chemical and biological properties of MTs. - Methods A total of 2322 observations from 47 studies were analyzed. - "Results Application of OAs increased total and available contents of N, P, Ca, Mg and total organic carbon (TOC) by 50-300%. MTs pH increased by up to 2.5 units due to the buffering effect of OAs associated with decarboxylation and input of base cations. Cation exchange capacity (CEC) of MTs increased by similar to 50%. Total, available, and extractable metal(loid) contents (e.g., Pb, Cu and Zn) decreased after OA addition by 25-90%, which was mainly related to a mass dilution effect, complexation, and precipitation. Basal respiration increased 10-fold, and enzyme activities increased from 50% to 2.5 times in the following order: phosphatase > dehydrogenase > arylsulfatase > beta-glucosidase > urease. This was associated with C inputs from OAs that are energy source for microorganisms and low metal(loid) toxicity by neutral-alkaline pH. Manure, compost, and biochar strongly increased pH, organic C, and CEC, and decreased available metal(loid)s. This was moderated by the pH and C/N of OAs, and the pH of MTs." - Conclusion Thus, applying OAs buffer pH and increase fertility in MTs, decreases metal(loid) toxicity, and stimulates microbial activity, which can accelerate restoration programs in mining activities.