Response of two lupin species to phytotoxic aluminium

The response of lupin species to phytotoxic aluminium (Al) was studied in Lupinus albus cv. Victoria and L. angustifolius cv. Gungurru, using L. luteus and Hordeum vulgare as tolerant and susceptible controls, respectively. Studies were done in nutrient solution and in soils with high Al content. In nutrient solution, nominal Al concentrations from 0 to 20 μM allowed discrimination of the response to Al among species. At 10 μM Al, root growth rates increased 90, 40 and 10% in L. luteus, L. albus and L. angustifolius, and reduced 75% in H. vulgare. Aluminium concentrations up to 80 μM stimulated citrate efflux from lupin species, but not from H. vulgare. In soils with 27% Al saturation and adequate phosphorus (P), the aerial biomass of lupins was not affected and was reduced 90% in H. vulgare. In this soil, addition of P did not affect shoot biomass in L. albus, and increased it 18% in L. angustifolius. When both species were grown in soils with Al saturation ranging from 0.1 to 42% and low P, addition of P increased shoot biomass by 22% in L. albus and by 131% in L. angustifolius, independent of Al treatments. According to these results, L. albus and L. angustifolius can withstand phytotoxic Al saturation of at least 42% in soils with adequate P supply. The response to this stress would depend on the ability of the species to acquire P from P-deficient soil. Citrate efflux by the roots would be at least one of the mechanisms used by both lupin species to tolerate phytotoxic Al in soils