Influence of certain herbicides and a forest fertilizer on the nitrogen fixation by the lichen Peltigera praetextata.

Effects of herbicides (Garlone 3A, MCPA, 2,4-D and Krenite) and nitrogen fertilizer (NH4NO3), commonly used in Swedish forestry, on nitrogen fixation (C2H2-reduction) by Peltigera praetextata (Sommerf.) Zopf. (field and laboratory) and its phycobiont Nostoc sp. (laboratory) were studied. The alga was affected by the herbicides 2,4-D and Krenite and the fertilizer, with a decrease in nitrogenase activity. Nitrogen fixation by the lichen was not affected by herbicides but treatment with NH4NO3 led to depression of nitrogenase activity and serious disturbance of the symbiosis, the latter effect due to the fertilizer's lethal effects on the mycobiont (electron microscopy).