**2. Phytomining**

As it was previously mentioned, the bioavailability and mobility of HMs in soil substrate are greatly influenced by the soil physicochemical properties (pH, Eh, electrical conductivity, cation exchange capacity, and soil mineralogy), the biological conditions, and the presence of soil inorganic and organic ligands. Careful risk assessments should be undertaken to select the appropriate hyperaccumulating plant species and determine safe and acceptable use of the aboveground plant biomass. As this aerial plant biomass gradually accumulates trace elements and other contaminants and its toxicity is likely to increase, it is important to select those hyperaccumulating species that are unlikely to enter the food chain or implement a protection system to avoid this important issue. There are several post-harvest management options for crops including energy generation, biofuel production, gasification, composting, recovery of critical and secondary raw material recovery, and phytomining.

**Phytomining or agromining** refers to the full agronomic process using hyperaccumulator plants as "metal crops." The process involves the farming of "metal crops" on subeconomic deposits or industrial or mineral wastes to obtain valuable element(s) from their harvested biomass *via* the production of a "bio-ore." However, defined considerations after implementing this management option should be given to ultimate the fate of chemical elements that have been concentrated in plant biomass along the phytomining process [1].

Microbial-assisted phytomining of HMs also represents a promising method for the remediation of contaminated soil [30]. Microbial-assisted phytomining of HMs involves several mechanisms such as biosorption, intracellular accumulation, enzyme-catalyzed transformation, bioleaching and biomineralization, and redox reactions [31]. In many cases, plant-microbe associations are highly efficient in absorbing, accumulating, translocating, and tolerating HMs because of their capacity to produce various substances that participate in stimulating growth and HMs accumulation (monocyclopropane-1-carboxylate deaminase, siderophores, indole acetic acid) [30]. In microbial-assisted phytomining, the exudates of mycorrhizal roots play a significant role in the efficiency of phytoextraction of the elements in the soil. For instance, concentrations of amino acids (glutamine, glutamic acid, valine, and methionine) and organic acids (citric acid, malic acid, and oxalic acid) in the root exudate of *Andropogon virginicus* were increased under P-deficient conditions [32], and the extraradical hyphae of AM fungi could exude diverse metabolites that are influenced by P levels and diverse AM fungal species [33]. In previous reports, we observed an increase in translocation for Mn, Fe, As, Zn, Ti, Cr, Cu, Rb, Sr., Al, Ba, K, and Ca when the MAP system based on the arbuscular mycorrhizal (AM) symbiosis established between the sunflower *Helianthus annuus* and the AM fungal species *Rhizophagus intraradices* (*GA5* strain, https://bgiv.com.ar/strains/ Rhizophagus-intraradices/ga5). The MAP system was applied for the recovery of critical and secondary raw material in sunflower plant biomass, and bioremediation of contaminated mining substrate [34, 35].
