Air pollution has emerged as a significant environmental issue in Tehran due to its detrimental effects. Nitrogen pollution stands out as a key air pollutant in the Tehran metropolis. Our research aimed to assess the reliability of cell membrane integrity in the lichen Xanthomendoza fulva as an indicator of acute nitrogen stress, to establish a quick and effective biomarker for monitoring the biological effects of acute nitrogen pollution. Two areas of Fasham (with low nitrogen load based on field observations) and Saad Abad (with high nitrogen load based on field observations) in the Tehran metropolis were selected for lichen sampling from tree bark. Due to the limited quantities of lichen in each area, a composite sample was collected, and 3 replications were taken. Nitrogen concentration in lichen thallus was determined using an elemental analysis method, and an increase in electrolyte leakage indicated the extent of cell membrane damage. The average nitrogen concentration in Fasham and Saad abad was 2.56 ± 0.16 % and 4.07 ± 0.09 %, while the average electrolyte leakage was 53.61 ± 1.21 and 65.66 ± 1.43 µSiemens/cm, respectively. The findings indicated a rise in electrolyte leakage due to cell membrane damage in the lichen Xanthomendoza fulva in the Saad Abad area, which is more exposed to various nitrogen compounds. The research also revealed a correlation between nitrogen levels and electrolyte leakage, emphasizing the influence of nitrogen on ion leakage, making it a useful marker for nitrogen stress. This native lichen, disappeared from numerous parts of the city of Tehran and limited to specific areas, effectively responds to pollution levels and atmospheric nitrogen exposure. It is recommended that this lichen be further investigated in future research regarding the monitoring of atmospheric nitrogen pollutant compounds.
