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Effect of some photosynthesis‐inhibiting herbicides on growth and nitrogenase activity of a new isolate of cyanobacteria, Nostoc G3

The effect of the photosynthesis‐inhibiting herbicides Goltix, Sencor, Tycor, Arelon, DCMU, paraquat and atrazine on growth and nitrogenase activity of a new isolate of cyanobacteria, Nostoc G3 was studied. Nostoc G 3 was cultivated under N2‐fixing photoautotrophic conditions. The used herbicide concentrations were in the range or recommended field rates. In the presence of Goltix (50 mg/l and 100mg/l), Arelon (15 mg/l und 30 mg/l), paraquat (10 mg/l and 20 mg/l) and DCMU (1 μM) the growth and nitrogenase activity of Nostoc G3 was almost completely inhibited. The most severe inhibitory effect was observed in the presence of paraquat. Even 1 h treatment of 1 mg/l paraquat caused a total inhibition of growth for 4 weeks. In contrast, the herbicides Sencor (10 mg/l and 20 mg/l) and Tycor (10 mg/l and 50 mg/l) did not cause inhibition of growth and nitrogenase activity. In the presence of atrazine (1 mg/l and 2 mg/l) the nitrogenase activity and the growth were partially inhibited. The results obtained in this study show that cyanobacteria occurring in natural environments are resistant against some of the photosynthesis‐inhibiting herbicides.