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

Abstract

Nitrogenase activity and CO2 fixation differed in two 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-ethyl-amino-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 x 10-7 M atrazine and 2.3 x 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).