Phosphorus enhances aluminium tolerance in both aluminium-tolerant and aluminium-sensitive wheat seedlings

Abstract

Seedlings growing in acid soils suffer both phosphorus (P) deficiency and aluminium (Al) toxicity stresses. An experiment was conducted to study the effects of Al and P interaction on Al-tolerant (ET8) and Al-sensitive (ES8) wheat genotypes in an acid soil. This study aimed to determine the interactive effect of Al and P in soil and within plant tissue. Three Al levels (0, 50 and 150 mg aluminium chloride [AlCl₃] kg⁻¹ soil) and five P levels (0, 20, 40, 80 and 160 mg P kg⁻¹) were used in this experiment. Bulk soil pH decreased with addition of AlCl₃ to the soil. Bulk soil pH increased at 160 mg P kg⁻¹ supply at three Al levels. Phosphorus supply reduced extractable Al in the soil in all Al treatments. Seedlings suffered more from Al toxicity in the absence of P supply. Increasing P supply resulted in increased seedling biomass under high Al toxicity. This high P ameliorated Al toxicity in the soil and may enhance ES8 growth under Al toxicity. The Al x P interaction affected the root and shoot P concentration in both genotypes and P supply had no effect on P translocation to the shoot. These results suggested that differential growth behaviour between ES8 and ET8 plays an important role in tolerance to Al toxicity irrespective of high P supply. It is concluded that the higher aluminium cation (Al³⁺) binding capacity in the root apoplast of ET8 seedlings contributes to its improved tolerance to Al toxicity compared to ES8 seedlings.

Keywords: Al x P interaction, apoplast aluminium, bulk soil pH, genotypic variation, rhizosphere pH

South African Journal of Plant and Soil 2013, 30(1): 13–21