Effect of Several Pesticides on the Growth and Nitrogen Assimilation of theAzolla-AnabaenaSymbiosis

Abstract

Of 15 pesticides evaluated in a screening test with respect to their effects on growth and nitrogen assimilation of theAzolla mexicana(Presl) –Anabaena azollae(Strasburger) symbiosis, the bipyridilium and phenolic herbicides at 0.1 ppmw were the most detrimental, causing up to a 75% reduction in nitrogen fixation and nitrate reduction with little or no effect on growth. Chloramben [3-amino-2,5-dichlorobenzoic acid] at 1.0 ppmw, and dicamba [3,6-dichloro-o-anisic acid], and benomyl [methyl-1-(butylcarbamoyl)-2-benzimidazolyl carbamate] at 10.0 ppmw caused an 84 to 99% reduction in nitrogen fixation without affecting nitrate reduction or growth. Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 10.0 ppmw stimulated nitrate reduction 20 fold, causing a 99% reduction in nitrogen fixation. Growth and nitrogen assimilation were reduced at similar concentrations between 0.1 and 10 ppmw for each of the other benzoic, triazine, dinitroanaline, and urea herbicides tested. Naptalam [N-1-naphthylphthalamic acid] was the only pesticide tested that had no effect on growth or nitrogen assimilation at 10.0 ppmw.