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 Mg(2+) and Ca(2+) activities, but not for Na+ and K+ activities. Higher H+ activity decreased the toxicity through H+ competition with Ni(2+) bound to biotic ligands at pH<7.0 or through the change of Ni species in solution at pH > or =7.0. When pH > or =7.0 the Ni(2+) plus NiHCO3+ were found to be toxic to barley root elongation. The conditional binding constants for Ni(2+), NiHCO3+, H+, Mg(2+) and Ca(2+) with biotic ligand were obtained: logK(NiBL), 4.83; logK(NIHCO)(3)(BL), 5.36; logK(HBL), 4.29; logK(MgBL), 4.01 and logK(CaBL), 1.60. It is suggested that in solutions with pH > or =7.0 free Ni(2+) as well as NiHCO3+, Mg(2+) and Ca(2+) competitions with Ni(2+), should be considered for BLM development.