## 2 Materials and Methods
### Analytical Methods
#### 2.4.2 Plant Sampling and Analysis  
For each pot, plant survival was determined 5 weeks after plantation (mid-term) and at the end of the experiment (week 8), according to equation (Equation (1)):  
\[Survival_{mid,\;end}\;(\%)=\frac{n_{Tmid,Tend}}{n_{T0}}\times 100 \tag{1}\]  
where:  
\(n_{T0}\): number of steam cuttings planted at the beginning of the experiment;  
\(n_{Tmid}\): number of surviving plants (i.e., with viable sprouts) at week 5 (mid-term);  
\(n_{Tend}\): number of surviving plants (i.e., with viable sprouts) at the end of the experiment (week 8).  
For each treatment, measurements were carried out considering all plants, without subsampling. Therefore, results are presented as cumulative values per treatment, and no variability measures (e.g., standard deviation or standard error) were calculated.  
Plant growth was evaluated after harvesting (week 8), considering new tissues produced by stems (Figure S3 Supplementary Materials). More specifically, the aerial growth was quantified considering sprout weight, and root growth was quantified considering root weight. The stems' weight was also evaluated. Plant specimens were harvested and rinsed with tap and distilled water. Fresh weight (FW, after carefully absorbing the rinsing water with paper) and dry weight (DW, after stove drying at 60 \({}^{\circ}\)C for 72 h) of roots, stems, and sprouts were determined. Trace metal content in stems and sprouts was determined according to standard methods [34]. Plant tissues were pretreated with oxygen peroxide and digested with aqua regia, and metal concentration was determined by ICP/OES (Optima DV 7000 ICP/OES, Perkin Elmer Inc.).  
The stage and the quality of rooting and sprouting were evaluated for each harvested plant, using a 0-4 scale. As reported in the literature, rooting quality is assessed by visual parameters for different species and using various attributing quality scores [36; 37; 38]. In this study, both for roots and sprouts, the evaluation scale was adapted to the plant studied (Table 1).  
At the end of the experiment (week 8), the content of photosynthetic pigments such as chlorophylls and carotenoids in leaves was determined and considered as an indicator of plants' health and tolerance to high metal concentration in substrates. Samples of leaves were randomly cut from plants (2 or 3 plants for each substrate), a quantity of 0.02-0.05 g (FW) was collected per plant and subsequently ground and mixed with ethanol (96%) in darkness for 12 h. The supernatant was analysed using a spectrophotometer (U-2000, Hitachi Ltd., Tokyo, Japan) at wavelengths of 470, 648.6 and 664.2 nm to determine the content of chlorophyll a (Chla) and chlorophyll b (Chlb), carotenes (Cc) and xanthophylls (Cx) according to the equations proposed by [39]. The concentration of total chlorophylls Chla+b was calculated as the sum of Chla and Chlb concentrations, and the ratio between chlorophyll types (Chla/Chlb) was also determined. The total concentration of carotenoids (Cx+c) was calculated as the sum of xanthophylls and carotenes. The ratio between total carotenoids and chlorophylls (Cx+c/Chla+b) was also calculated.