## 2 Materials and Methods  
### Experimental Design  
Six hundred kilograms of an acidic metal-contaminated mine soil (0-20 cm in depth) was obtained from an abandoned area of Dabaoshan pyrite/copper mine. Detailed information about the acidification properties and heavy metal concentrations in this mine soil were reported in our previous study [17]. To correct the soil acidity, two levels of lime (25 t ha\({}^{-1}\) and 50 t ha\({}^{-1}\)) were applied according to the soil lime requirement to produce final pHs of 5 and 7, respectively. Lime, NPK compound fertilizer (N-P\({}_{2}\)O\({}_{5}\)-K\({}_{2}\)O = 15:15:15), phosphate fertilizer and river sediment were applied as amendments in this study. The lime and fertilizers were produced by Shijiazhuang Sanyuan Compound Fertilizer Plant. Sediment from the Pearl River was collected from the place without water cover. The mine soil and river sediment were air-dried, thoroughly homogenized, sieved (5 mm) and stored in the laboratory for 6 months before pot experiment started. Selected physico-chemical properties of the mine soil and river sediment are shown in Table 1. The mine soil, lime, NPK compound fertilizer, phosphate fertilizer and river sediment were mixed at pre-determined ratios which were presented in Table 2. Two controls without amendments [control1 (mine soil) and control2 (mine soil + sawdust)] were also established. 200 g dry sawdust was applied to all the soil treatments to improve porosity, except for control1. All the treatments were replicated four times with four pots (1.7 kg per pot) and placed in a glasshouse, where day/night temperatures were maintained at 22-30/10-16 \({}^{\circ}\)C. The soil mixtures were then adjusted to 70% of their maximum water holding capacity and allowed to equilibrate for 2 weeks prior to sowing. A mixture of seeds of _Sebania cannabina_ Poir., (10 seeds per pot) _Lygeum spartum_ Loefl.ex L. (20 seeds per pot) and _Cynodon dactylol_ (L.) Pers. (30 seeds per pot) were worn on each pot. The pots were watered once three days to maintain their initial water content and the plants allowed to grow for 6 months in the glasshouse (Figure S1, Supplementary information). At the end of this growth period, plants were carefully removed from the pot and all the soil in the pot was collected. The soil samples from each treatment were divided into two subsamples. One fresh subsample was stored at 4 \({}^{\circ}\)C for microbial community and enzyme analysis within two weeks; the other subsample was air-dried and subjected to chemical analysis. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Mine Soil** & **River Sediment** \\ \hline Sand (\%) & 82.2 \(\pm\) 9.7 & nd \\ Slit (\%) & 10.1 \(\pm\) 0.89 & nd \\ Clay (\%) & 7.5 \(\pm\) 0.43 & nd \\ pH & 2.5 \(\pm\) 0.14 & 7.3 \(\pm\) 0.29 \\ Electrical conductivity (dS m\({}^{-1}\)) & 3.1 \(\pm\) 0.18 & 1.6 \(\pm\) 0.13 \\ Organic matter (g kg\({}^{-1}\)) & 6.2 \(\pm\) 0.53 & 70.6 \(\pm\) 12.1 \\ Total nitrogen (mg kg\({}^{-1}\)) & 44.5 \(\pm\) 3.6 & 1054 \(\pm\) 88.1 \\ Total phosphate (mg kg\({}^{-1}\)) & 307 \(\pm\) 25.2 & 722 \(\pm\) 53.2 \\ Total potassium (mg kg\({}^{-1}\)) & 290 \(\pm\) 16.4 & 2717 \(\pm\) 217 \\ Zinc (Zn, mg kg\({}^{-1}\)) & 1175 \(\pm\) 84.1 & 147 \(\pm\) 16.8 \\ Lead (Pb, mg kg\({}^{-1}\)) & 1107 \(\pm\) 67.9 & 75.1 \(\pm\) 10.4 \\ Copper (Cu, mg kg\({}^{-1}\)) & 1826 \(\pm\) 121 & 50.4 \(\pm\) 8.8 \\ Cadmium ( Cd, mg kg\({}^{-1}\)) & 2.6 \(\pm\) 0.33 & 0.76 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selected physico-chemical properties of the mine soil and river sediment used in the pot experiment.