Figure 5. Nodule number and nitrogenase activity.

Nodule number (A) and nitrogenase activity (B) of M. lupulina inoculated S. meliloti or a combination of S. meliloti and A. tumefaciens under moderate (200 mg kg⁻¹) or severe (400 mg kg⁻¹) Cu or Cu (400 mg kg⁻¹) and Zn (400 mg kg⁻¹) double stress conditions. –No nodule was observed. The values indicate the means ± SE of three replicates. Bars carrying different letters denote differences on the basis of a t-test (p < 0.05).