## 3 Results and Discussion
### Sorghum Metal Transfer on the TE-Contaminated Site and Biomass Quality  
#### 3.3.1 Sorghum Effect on the TE Extractable Fraction  
The pH values measured on all plots, throughout the study, were slightly alkaline, situated around 8 (Supplementary Figure S1), even though the two sorghum cultivars seemed to slightly lower the sediment pH (\(p<0.05\)) as a consequence of H\({}^{+}\) excretion by the root system during the absorption of nutrients (NH\({}_{4}\)+) [49]. Before sorghum cultivation, the average extractable Cd, Cu, Pb, and Zn concentrations measured in the sediment were 0.03, 0.48, 0.06, and 5.16 \(\mu\)g g\({}^{-1}\) dry sediment (DS), respectively. These concentrations were between 2.5 to 27 times higher than the reference value reported in the standard ISO 19730:2008 (E) (Figure 2A,B) [42]. The culture of Biomass 133 did not modify the extractable Zn concentrations measured in the sediment in areas 1 and 3 (Figure 2A), while a slightly negative effect of the cultivar was evidenced in area 2 (\(p<0.05\)), with an increase in the extractable Zn concentration (Figure 2A). For Cd, a positive effect of the cultivar was observed in area 3, the area with the highest extractable concentration (Figure 2A). Concerning the cultivar Trudan HL, an adverse effect of the cultivar was only found on area 3 for Zn and Cd, with extractable concentrations being higher at harvest than at the beginning (Figure 2B, \(p<0.05\)). In contrast to Zn and Cd, extractable concentrations of Pb and Cu (Figure 2A,B) did not show a statistical difference (\(p>0.05\)) in any of the studied areas for either of the cultivars, which could be related to their closer value to the references even before cultivation, rather than to a selective effect of the cultivars. The absence of a clear effect of the cultivars on metal extractability in the sediment, according to the areas and TE, indicated that both cultivars had no or a small impact on this parameter in our experimental conditions. The percentage (%) of mobile TE calculated as extractable concentrations over total concentrations is evidenced by the following order of mobility, Pb \(<\) Zn\(<\) Cd\(<\) Cu, irrespective to the cultivars and the areas (Supplementary Table S2). Negative correlations between pH and TE extractable concentrations were demonstrated (Cd: \(p<0.001\), r = \(-0.36\); Cu: \(p<0.05\), r = \(-0.23\); Pb: \(p<0.05\), r = \(-0.22\); Zn: \(p<0.001\), r = \(-0.60\)), indicating that a pH decrease could increase the TE extractable concentration and explain the small significant variations found for some TEs. With regard to sediment deposit management, and in the particular case of field studies with high sediment TE contamination, it could be advised to maintain the pH around 8 to minimize the TE mobility in the sediment and limit the TE transfer in the environment [28; 50]. To reduce extractable concentrations, especially for Cd and Zn, coupling sorghum to an amendment that would maintain pH at 8 could achieve this objective. The addition of an alkaline amendment that does not modify the sediment pH, like biochar, could also reduce the Cd extractable concentration by the creation of a stable complex with iron or manganese oxides or by adsorption [51; 52]. As sorghum is known to be mycorrhizal, the addition of an arbuscular mycorrhizala fungi (AMF) inoculum could \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Area 2** & **Yield (kg/25m\({}^{2}\))** & **Yield (t ha\({}^{-1}\))** & **Yield (t ha\({}^{-1}\))** & **Duration of Growth (Day)** & **Height (m)** \\ \hline Sorghum Biomass 133 & 137.43 & 54.97 & 21.75 & 131 & 3.39 (\(\pm 0.21\)) \\ \hline Reference Biomass 133 [40] & - & - & 20.7 & 105–125 & 3.5 \\ \hline Sorghum Trudan 1 HL & 80.97 & 32.38 & 9.85 & 105 & - \\ \hline Reference Trudan HL [41] & - & - & 10–15 & 60 first cut and 30 s & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Biomass yield, growth duration, and height of sorghum in area 2, FM: fresh matter, DM: dry matter.