Phytoremediation. Electric conductivity. Heavy metals. Luvisoi

Phytoextraction is an efficient remediation technique for abiotic stresses caused by heavy metals and excess salts in the soil. The halophyte Atriplex nummularia has been used in phytoextraction programs for soils affected by salts and with indications of heavy metal use. However, the potential for heavy metal extraction by Atriplex is still unknown. In this regard, this research aims to evaluate the tolerance of Atriplex nummularia to cadmium (Cd), as well as the influence of salinity on the phytoextraction process. An experiment was conducted to assess the effect of salinity using two soils of the same order, Luvissol, with absence and presence of saline character, and six concentrations of Cd (0, 10, 20, 30, 40, and 50 mg/kg). The experimental design was a randomized block design in a 2 (absence and presence of salinity) x 6 (Cd doses) factorial arrangement with four replications. Biometrics (height, fresh and dry biomass of shoot and roots), Cd content in the shoot (leaf+stem) and roots, Cd translocation factor, Na+ and Cl content in the shoot, leaf gas exchange (net photosynthesis, stomatal conductance, transpiration, water use efficiency, and intrinsic water use efficiency), leaf water potential, osmotic potential, pressure potential, osmotic adjustment, relative water content, leaf succulence, chlorophyll a fluorescence, and photosynthetic pigments (chlorophyll a, b, and carotenoids) were evaluated. Plants grown in saline soil showed lower values of water and osmotic potential, as well as higher values of osmotic adjustment compared to those grown in non-saline soil. The dry biomass of the shoot was not affected by Cd doses in non-saline soil. However, for saline soil, the relative yields compared to the control dose were 75, 57, 45, 39, and 40% for 10, 20, 30, 40, and 50 mg/kg of Cd, respectively. Nevertheless, the yields of Atriplex up to the dose of 30 mg/kg of Cd were higher in saline soil, possibly indicating an additive effect of saline stress and Cd dose > 30 mg/kg. Regarding physiological variables, no effect of Cd on leaf water potential was observed, indicating that turgor was not responsible for any yield reductions. However, reductions in net photosynthesis, stomatal conductance, and transpiration were observed with increasing Cd doses. Nonetheless, water use efficiency (WUE) was higher under salinity conditions. The average Cd content in the shoot of Atriplex was 49 and 25 mg/kg for saline and non-saline soil, respectively, indicating the positive influence of salinity on the Cd accumulation potential. Soil salinity optimized the Cd translocation factor. The results of this research confirm the enhancing effect of salinity on the Cd accumulation process by Atriplex nummularia and the influence of soil salinity, as well as the natural Cd tolerance capacity of Atriplex. Due to the lack of physiological data associating salinity and heavy metal, this research will be of great relevance for more specific Cd phytoextraction studies.