Development of a biotic ligand model (BLM) predicting nickel toxicity to barley (Hordeum vulgare)

A biotic ligand model (BLM) was developed to predict nickel toxicity, affecting root growth of barley (Hordeum vulgare), in nutrient solutions. The extent to which Ca²⁺, Mg²⁺, Na⁺, K⁺ ions and pH each influenced nickel toxicity was determined. Higher activities of Mg²⁺ linearly increased the 4 d EC50_Nl²⁺, while Ca²⁺, Na⁺, K⁺ and H⁺ activities did not significantly influence Ni²⁺ toxicity. Stability constants for the binding of Ni²⁺ and Mg²⁺ to the biotic ligand were obtained: log K_NiBL = 5.27 and log K_MgBL = 3.47. Further, it was calculated that on average 57% of the biotic ligand sites needed to be occupied by nickel to induce 50% root growth inhibition. Auto-validation of the BLM indicated that predicted EC50s differed from the observed EC50s by a factor of less than 2, indicating that the BLM concept may also be used to predict metal toxicity to terrestrial plants.