## 3 Results and Discussion
### Pot Experiments

Table 3: Element concentration (mg/kg) \(\pm\) SD in Campana and Nobile soils, after adding a 30% portion of soil improver (Floraewiva (FW)), and in FW, before starting the experimentation (t\({}_{0}\)). Under these conditions, the same happens in roots. However, As lowers in roots growing in NOB soils without FW. These results are not unexpected since this species was chosen on the basis of previous studies that assessed its capability to absorb both arsenate and arsenite [42]. Arsenate is an analogue of phosphate (P), so arsenate is taken up via the P transporters in higher plants including _P. vittata_[43], and it competes with P uptake. The uptake mechanism of arsenite by _P. vittata_ is mainly controlled by a transporter-mediated active process. Since arsenite often occurs as a neutral species in the environment, it has been hypothesized that arsenite is taken up by plants via aquaporin channels [44]. With respect to Pb, one of the major pollutants, results suggest that the plants used for phytoextraction did not have a  
Figure 2: Score and loading plot from principal component analysis (PCA) (PC1 vs. PC2) on element concentration data of (**a**) epigeal and (**b**) hypogeal parts. NOB = plants grown in Noble soil, CA = plants grown in Campana soil, yellow spot = addition of FW to the soil, blue spot = no addition of FW, p = _Pteris vittata_, b = _Brassica juncea_, h = _Helianthus annuus_, z = _Zea mays_. strong uptake efficiency, although _B. juncea_ was suggested for the phytoremediation of lead. However, the main obstacle to the Pb phytoextraction could be its low bioavailability. It was estimated that only 0.1% of total soil Pb is amenable for extraction [45] and, in most cases, the addition of chelating agents (e.g., ethylene diamine tetra-acetate (EDTA) anion) in aqueous solutions was commonly required to mobilize Pb and facilitate its extraction [19; 46]. In the absence of a chelating agent, the mobility of lead remains very low and it cannot be effectively extracted. When comparing the absorption of elements in the epigeal part of selected plants grown in the presence or absence of FW, _B. juncea_ and _H. annuus_ take up more Cd, Zn, Cu and Co without soil improver, although the difference is not marked. On the other hand, the behavior of _Z. mays_ is very different and its effectiveness is strictly connected to the addition of the soil improver. This renders this plant species more efficient towards elements with negative loadings on the PC2, such as As, Pb, Ni and Cr. Figure 3 shows the values of bioconcentration factors of plants grown in Campana (a, b) and Nobile (c, d) soils for PTEs, and the results obtained by the PCA are confirmed. _P. vittata_ shows an excellent bioconcentration ability--its action is particularly marked for As and Pb, but it is also efficient for other PTEs to become one of the most capable species for lead uptake. The ANOVA and Tukey tests (Table S4, Supplementary Materials) confirm a significant difference between the BF values of _P. vittata_ for As and those of all other plants. Overall, _H. annuus_ and _Z. mays_ are more efficient than _B. juncea_ in the uptake of Zn and Cu and _B. juncea_ shows a good capability in the cadmium absorption. The FW addition determines a change in the bioconcentration capacity of plants for phytoremediation, probably due to the input of organic carbon that decreases the mobility and bioavailability of PTEs [35]. Indeed, although _P. vittata_ always  
Figure 3: Bioconcentration factors (BFs) of plants chosen for phytoremediation and grown in (**a**) Campana without FW, (**b**) Campana with FW, (**c**) Nobile without FW and (**d**) Nobile with FW. Values are expressed as mean \(\pm\) SD. shows a greater ability to absorb all elements, the absolute value of As is much greater in the absence of FW, _Z. mays_ is less efficient in the uptake of all the elements, whereas _H. annuus_ shows approximately the same efficiency. Cd is adsorbed in slightly higher concentration by _B.