Phytotoxicity of aluminium to wheat plants in high-pH solutions

Phytotoxicityof aluminiumin acid soils is well known.At pH :::::6.3a,luminate [A1(OH)4-]is the principal hydroxo-aluminium species in soil solutions; however,its phytotoxicity has not received much attention. Sodic subsoils in Australia are generally alkaline and have pH above 9. During our survey of 8 subsoils in South Australia, we found aluminate ions at concentrations greater than 0.8 mg/L (29.7 /lmol/L of aluminium)in soil solutions when pH was greater than 9, with corresponding high uptake of aluminium by wheat plants. We studied the phytotoxicity of aluminium to wheat plants in solution culture by maintaining the pH of alkaline solutions at 9.2. Relative root lengths ofwheat plants, compared with those in reverse-osmosis deionised water,were significantIy reduced in alkaline solutions and COrfree air indicated toxicity ofhydroxy, carbonate and bicarbonate ions. Further reduction of root lengths due to aluminate toxicity was also evident. Relative root lengths of wheat plants, when comparing between +aluminium and -aluminium treatments, were reduced up to 50