Refining a biotic ligand model for nickel toxicity to barley root elongation in solution culture

The effects of widely ranged pH and some cations on nickel (Ni) toxicity to barley root elongation were determined using a biotic ligand model (BLM) in solution culture. The results showed that Ni toxicity decreased with increases of Mg2+ and Ca2+ activities, but not for Na+ and K+ activities. Higher H+ activity decreased the toxicity through H+ competition with Ni2+ bound to biotic ligands at pH<7.0 or through the change of Ni species in solution at pH≥7.0. When pH≥7.0 the Ni2+ plus NiHCO3+ were found to be toxic to barley root elongation. The conditional binding constants for Ni2+, NiHCO3+, H+, Mg2+ and Ca2+ with biotic ligand were obtained: log KNiBL, 4.83; logKNiHCO3BL, 5.36; log KHBL, 4.29; log KMgBL, 4.01 and log KCaBL, 1.60. It is suggested that in solutions with pH≥7.0 free Ni2+ as well as NiHCO3+, Mg2+ and Ca2+ competitions with Ni2+, should be considered for BLM development.