Lichens can help scientists monitor pollution by using nitrogen from the atmosphere, but it's not clear how well they absorb ammonium and nitrate, which are forms of nitrogen.
A research study tested how well lichens take in ammonium and nitrate under different conditions, finding that they prefer ammonium and absorb it more efficiently than nitrate.
The study also showed that more ammonium in the water makes it harder for lichens to absorb nitrate, especially in the dark, which is important for understanding how to use lichens to check nitrogen pollution levels.