Nitrogen fixation, and hence the abundance of lichen and their host plants, may be decreased by application of nitrogen-based agricultural fertilizer and by atmospheric pollution.
[1][2] While it does not occur often, formation of akinetes (type of cell formed by cyanobacteria which are resistant to cold and desiccation) was observed in nitrogen fixing lichen.
[5] The nitrogen fixation is energetically costly due to chemical transformation and only about 10% of lichen are partnered with cyanobacteria.
[8] Ammonium, nitrate and organic nitrogen can be assimilated by lichen along with phosphorus as an important stimulant for cyanolichens.
According to the experiment by Sparrius et al., when nitrogen fertilizer was added into the soil, lichen cover was reduced by ~50%, while the addition of phosphorus showed opposite result.
[9] In the region such as boreal forest, where nitrogen and phosphorus are limiting nutrients and for symbiotic interaction to occur properly, their ratio must be balanced.
[8] General pollution of climate that is indicated by the concentration of nitrogen oxides can also affect the growth of lichen.
[10] When compared to bryophyte (non-vascular land plant), which is also sensitive to nitrogen fertilizer, lichen showed a much stronger response.
[3] Some lichen species are able to refrain from assimilating excessive amount of nitrogen in order to maintain a balanced tissue concentration.
[3] Majority of lichen species absorbs more NH4+ than NO3- and the impact of temperature on the rate of fixation is "consonant to the normal enzymatic kinetics of them".
[11] Upon nitrogen fixation, there will be an increase of algal cell growth, chlorophyll concentration, and photobiont population.
There are certain regions in the world that most plants cannot live due to harsh environments as well as lack of nutrients such as nitrogen.
Lichen is able to absorb nitrogen in multiple forms from soil, rock, and air, taking a part in carbon cycle at the same time.
[5][6] The industrial nitrogen fertilizer greatly affected the vegetation and agriculture throughout the world, resulting significantly increased the amount of food with better quality, but it has a negative impact on ecology in the long run.
According to an experiment, the ammonium toxicity due to nitrogen deposition reduced the vitality of lichen greatly at different regions such as inland dunes, boreal conditions, and subarctic heaths.