The Effects of Some Herbicides on Nitrogenase Activity and Carbon Fixation in Two Subarctic Lichens

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Abstract
Nitrogenase activity and CO2 fixation differed in 2 subarctic lichens, Peltigera aphthosa (L.) Willd. and Stereocaulon paschale (L.) Fr., after exposure to 10-8-10-4 M concentrations of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea), or ioxynil (4-hydroxy-3,5-diiodobenzonitrile). Nitrogenase activity in P. aphthosa was stimulated at 4.7 .times. 10-7 M atrazine and 2.3 .times. 10-8 M ioxynil but not in S. paschale. Inhibitions of nitrogenase activity in P. aphthosa at the highest concentrations of diuron, atrazine and ioxynil were 90, 80 and 30%, respectively. In S. paschale, high concentrations of ioxynil completely inhibited nitrogenase activity, while diuron caused 50% and atrazine 35% deactivation. Positive net carbon assimilation in P. aphthosa was found after exposure to 10-6-10-8 M atrazine or diuron, but in S. paschale, only at 10-8 M diuron. Increased respiration in light was observed in S. paschale after exposure to diuron, ioxynil and atrazine (10-4 M) and in P. aphthosa after exposure to ioxynil (10-4 M).

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