Effects of Aluminum Toxicity on Wheat Plants Cultivated Under Conditions of Varying Ionic Strength

Abstract

The effects of aluminum (Al) toxicity on growth of Triticum aestivum, cv. Atlas 66, were studied under varying conditions of solution electrical conductivity (EC). In solutions containing only 400 μM CaCl2 (low EC) with daily nutrient additions (0.20 g nutrient g plant−1 day−1), severe Al toxicity was observed at 20 μM Al. In more conventional nutrient solutions containing 3600 μM N and all other essential nutrients in optimal proportions (high EC), more than 200 μM Al was required to reduce plant mass production below 50% of control. Solution pH increased in both high and low EC solutions as a result of plant growth, but the effect was counteracted by Al toxicity. In low EC solutions (with daily nutrient additions), EC remained stable with time in the treatments without Al, reflecting a balance between the relative addition rate (RAR) of nutrients and the relative growth rate (RGR) of plants. In the presence of Al, solution EC increased as Al toxicity reduced the RGR of plants below the RAR. In high EC solutions, EC values decreased with time in all treatments as plant growth depleted fixed nutrient stocks. The extent of decline in EC was proportional to plant growth over the experimental period. The results of this study demonstrate that Al is more toxic when solution EC is maintained at low levels using the relative addition rate (RAR) technique. In contrast to high EC treatments, low EC treatments provided a growth response that was more consistent with those observed under field conditions. Use of the RAR technique and low EC conditions should be considered in future experiments.