Ionomic analysis of Prosopis laevigata response to heavy metals: phytoremediation potential determined by wavelength-dispersive X-ray fluorescence

Abstract

Prosopis laevigata (mesquite) plants can tolerate drought, thermal stress, alkalinity, salinity, and toxicity of heavy metals, making them attractive for phytoremediation. Nonetheless, most of these features have been studied under controlled laboratory conditions. In this work, the bioaccumulation of heavy metals in a free-living population of P. laevigata trees growing in a heavily metal-contaminated site (aluminum, chromium, iron, titanium, copper, and zinc) was analyzed. Furthermore, crystal phases of mineral nutrients and trace elements found in P. laevigata tissues were determined by X-ray diffraction. P. laevigata trees accumulated 705 (± 17), 47,064 (± 1459), 14,800 (± 401) and 30,000 (± 1719) mg/kg of Cu, Zn, Fe and Al, confirming the potential of these plants to hyper-accumulate metals. The X-ray diffraction analysis showed that P. laevigata trees can chelate Al3+ with phosphates to form orthorhombic crystals of aluminum phosphate (AlPO4) in the tissues. This aluminum chelation was probably a mechanism of tolerance used by the plant. The inoculation of seedlings with the endophytic Bacillus cereus MH778713 did not prevent Cr-accumulation in the plant but increased metal tolerance and seedling development. These results highlight the use of P. laevigata and B. cereus MH778713 together as tools for heavy metal bioremediation, particularly on arid and semiarid soils.