Cultivar-specific differences in heavy metal (Cd, Cr, Cu, Pb, and Zn) concentrations in water spinach (Ipomoea aquatic 'Forsk') grown on metal-contaminated soil

This study aimed to investigate the cultivar differences and the involved rhizosphere mechanisms in multiple heavy metal (i.e., Cd, Cr, Cu, Pb, and Zn) accumulation in water spinach. Pot experiments were performed on long-term contaminated soil to determine heavy metal accumulation in 15 water spinach cultivars. A hydroponics experiment was extended using Ca channel blocker LaCl3. Nearly two-fold variations of heavy metal concentrations were found among the 15 cultivars. Cd, Cr, Cu, and Pb concentrations positively correlated with Ca and Zn concentrations. LaCl3 significantly reduced the phyto-uptake of Cd and Cr. The cultivar differences in heavy metal accumulation coincided with the concentration variation of metals activated by low molecular weight organic acids (LMWOAs) in the rhizosphere. Temperature and soil salinity clearly affected the cultivar differences in heavy metal accumulation. Ca uptake and LMWOA secretion serve a crucial function in the variation of heavy metal accumulation among water spinach cultivars. Temperature and soil salinity should be prioritized in cultivar screening.