Effects of cadmium and copper on the biologic fixation of nitrogen by acacia cyanophylla lindl

The seedlings of acacia cyanophylla were treated with different doses of Cu and Cd. The study of the accumulation of these heavy metals by the plant indicates that for the same dose, the endogenous levels are more elevated with Cd than with Cu. This indicates the strong mobility of Cd and constitutes one of the important reasons of its toxicity. The obtained results reveal that at low doses, Cu involves a strong decrease of the number and the weight of the nodules but the viability is affected only with the strong doses. On the other hand, Cd at low dose, affects both the processes of the nodulation and that of the viability of nodules. The measurement of the symbiotic nitrogen fixation, using the method of isotopic N dilution showed that at low doses (10 and 20 ppm), the N2 fixation is more affected by Cd than by Cu. At strong doses (50 ppm), the two types of metals inhibit completely the N2 fixation on acacia cyanophylla (author)