Figure 2.

Calculated root responses to CaCl₂, MgCl₂, and toxicants in the rooting medium. [CaCl₂] + [MgCl₂] = 1 mm and pH = 4.5, except where H⁺ was the designated toxicant. Toxicant levels (AlCl₃ = 3.06 μm, pH = 4.12, and NaCl = 132.2 mm) were chosen so that RRL_max = 50 at [CaCl₂]/([CaCl₂] + [MgCl₂]) = 0.5. ψ₀ was −14, −15, and −10 mV for the added Al³⁺, H⁺, and Na⁺, respectively. The constancy of ψ₀ for a toxicant means that electrostatic displacement of toxicant by Ca²⁺ (mechanism I) played no role in the computed trends. A₂ = 1 − 1/exp[(a₂{Ca²⁺}₀)^{b₂] and is an expression of mechanism II alleviation. The continued increase in} RRL_max for Na⁺ and H⁺ in the top panel signifies the action of mechanism III.