## 3 Results and Discussion
### Effect of the Addition of Biochar Materials on Se Uptake from Soil and Its Phytoextraction  
Se levels significantly increased in plants growing in Se-treated soil at different concentrations: 1-3 mg/kg and registered an average value of 11.7 mg/kg compared to 0.415 mg/kg in control plants growing in non-contaminated soil (Figure 1). This result demonstrated an efficient translocation of Se from soil to plants and a significant accumulation of Se proven by a BAF value of 8.8, superior to the 0.5 obtained for non-treated plants (Figure 3). This confirms the capacity of _Pileum_ species to uptake and translocate selenium from soil and then to bioaccumulate it to much higher levels over time. The good translocation and accumulation of Se in plants were also confirmed by a significant positive correlation between selenium in plants and selenium in soil with a correlation coefficient r of 0.759, coefficient of determination R\({}^{2}\) of 0.577, and \(p\) value of 0.00412. These statistical results demonstrated the efficiency of _Pileum_ plants as a Se secondary accumulator species which can be further used for Se phytoremediation, especially in the Nordic context. Moreover, these levels of Se in plants were significantly correlated with soil parameters, mainly pH, redox potential, organic matter, cations including Ca, K, Mg, Na, metals, chiefly Al, Cr, Fe, Mn, Co, Pb, and also anions, mostly Cl\({}^{-}\) and SO\({}_{4}\)\({}^{2-}\) (Table 2). However, no correlation was observed between Se content and Ni (r = 0.399) and NO\({}_{3}\)\({}^{-}\) (r = 0.249) in soil. These findings were previously confirmed by [PERSON] et al. [40] and [PERSON] et al. [41] who revealed the dependence of Se plant uptake on sediment factors, mainly pH, redox conditions, organic matter, sediment texture, Se content in the soil, and competing anions. Then, the investigation of the statistical correlation between Se levels in plants and other parameters such as anions, heavy metals, and cations in plants demonstrated that Se in the plant was significantly positively correlated to anions concentrations (Cl\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), NO\({}_{3}\)\({}^{-}\)) with an r of 0.92, R\({}^{2}\) of 0.85 and \(p\)-value of 0.004769. However, a low correlation between Se in plants and heavy metals and cations concentrations in plants was noted. Thus, Se in plants was significantly correlated to the above anion concentrations but not to heavy metals and cations. The correlation between Se and nitrogen was previously confirmed by [PERSON] et al. [42] who showed that nitrogen increases Se uptake and translocation to plants given that nitrogen increases sulfur assimilation. Consequently, plants could absorb Se and sulfur using the same metabolic pathway involved in the activation of O-acetyl serine which induces the synthesis of cysteine and selenoproteins. Also, high concentrations of nitrate cause Se anions to be released in soil, which permits Se uptake by the plants [43]. Cations usually show this antagonistic effect on Se as they are considered essential nutrients for plant growth and therefore Se competes with them [44]. Furthermore, the antagonistic  
Figure 2: Soil parameters such as electrical conductivity, oxygen redox potential, pH, dissolved oxygen, and organic matter at different Se concentrations (1, 2, and 3 mg/kg) using different quantities of materials: 10 and 50 g of activated biochar and 10 g of pristine biochar collected at the end of the greenhouse experimental device. effect of Se with heavy metals was previously reported by [PERSON] et al. [45] who noted it chiefly for As and Se depending on their levels in soil, their chemical forms, and plant genotype. They can be uptaken by the root system via the same transporter, showing a competitive interaction that minimizes the translocation to shoot of one of them. Furthermore, the addition of both biochar and activated biochar to soil decreased the Se uptake by plants.