Interactive effects of UV-B and pesticides on photosynthesis and nitrogen fixation of Anabaena doliolum

The effects of UV-B and commercial grade pesticides (butachlor and carbofuran), individually and in combination, were studied on a variety of physiological processes of rice field cyanobacterium Anabaena doliolum. Butachlor was found to be 2-12% more toxic than carbofuran and 4-24% than UV-B on the growth, photosynthesis, lipid peroxidation, membrane permeability, and nitrogenase activity of the test cyanobacterium. Of the three photosynthesis inhibitors, the butachlor-induced inhibition of whole chain was approximately 3 and 21% higher than carbofuran and UV-B, respectively. Although the interaction of the stress factors caused a significant inhibition (P<0.01), it was still less than the additive effect on the parameters investigated, except for PSI.