Influence of environmental factors and exogenous nitrogen on nitrogen fixation by intact thallus and excised cephalodia of Peltigera aphthosa

The present study investigates the effects of various abiotic environmental factors: air humidity, moisture content, oxygen and exogenously supplied nitrogen on acetylene reduction by intact thallus and excised cephalodia of Peltgera aphthosa. Intact thallus and excised cephalodia of Peltigera aphthosa were incubated at various conditions of air humidity, moisture contents, oxygen tensions, and addition of exogenous nitrogen, and comparative nitrogen fixation by the intact thallus and excised cephalodia was used as a method for assessment. Acetylene reduction (nitrogen fixation) was enhanced at conditions of lowered oxygen tension and at initial addition of nitrogen to the medium. However, prolonged incubation of Peltigera aphthosa in the medium with combined nitrogen addition resulted in fluctuation of nitrogenase synthesis. Acetylene reduction rates were stimulated in an atmosphere of 100% relative humidity (RH) and moisture content range of 570-620% of dry weight of Peltigera aphthosa. The decrease of nitrogenase activity measurable by acetylene reduction of thallus after prolonged incubation in the medium with combined nitrogen addition shows susceptibility of the symbiosis (lichen) since the thallus showed signs of disintegration at this time. Furthermore, air humidity and moisture content of the thallus influenced nitrogenase synthesis of Peltigera aphthosa considerably on separation of cephalodia such approach decreased nitrogenase activity and also elicited differences in their response to the various treatments. Applicability of this technology would enhance plant sustainability and yield in agricultural farms.