Interaction between aluminium and phosphorus in sorghum plants

A solution culture experiment was carried out to study the effects of interactions between aluminium (Al) and phosphorus (P) on Al-toxicity under conditions of suboptimal P supply. The experiment was conducted in a growth chamber with seedlings of the Al-sensitive sorghum genotype TAM428 (Sorghum bicolor (L.) Moench). Phosphorus deficiency differed from Al toxicity in its effect on shoot/root ratio and root morphological charateristics. Results indicated that there were positive effects of Al on the uptake and assimilation of P. Therefore, it was unlikely that an Al-induced P deficiency could account for the observed reduction in plant biomass. Plants suffered more from Al toxicity at very low P supply. Moreover, decreasing P supply resulted in increased root H-ion efflux density. In the soil, where a rhizosphere can be formed, this would make the plant even more susceptible to Al. Dry matter yield of the plants was affected more severely by Al at the first harvest (14 days) than at the second (35 days), but the opposite was true for P. Aluminium-inhibited root development and reduced uptake of N, K and Mg (but not Ca) may be partly responsible for the growth depression. Increasing the P supply exerted certain roles in eliminating Al phytotoxicity, possibly through improved root development and nutrient uptake. The detrimental influence of Al on biomass could be overcome by doubling the P supply.