One species of lichen from each of three different families (Collema wyomingensis , Caloplaca elegans (Link)T. Fries, and Parmelia molliuscula Ach.) was studied to determine whether or not these lichens can fix atmospheric nitrogen. Samples of these three lichens were collected in the early spring of 1967. Samples of each species were placed in 20-ml glass tubes which contained 5 ml of glass wool saturated with 0.5 M nitrogen-free Hoaglands nutrient solution. These tubes were sealed by heat onto a gas manifold system and evacuated. An N15- enriched atmosphere (22 atoms % N15) was introduced into the tubes from the gas manifold system. The tubes were sealed off with heat and placed in a growth chamber for seven days with alternate twelve hour periods of light and dark with temperatures of 25 degrees C. and 18 degrees C., respectively. At the end of the incubation period the lichen samples were subjected to a modified micro-Kjeldahl analysis in order to convert the tissue nitrogen to ammonium sulfate. The ammonium sulfate was treated with strong base to release the ammonia, which in turn was dehydrogenated over hot cupric oxide. The freed nitrogen was collected in 15-ml collection bulbs and the contents were scanned in a mass spectrometer for the presence of an increased percentage of N15. The results showed no fixation of atmospheric nitrogen by any of the three species of lichen. Further research on atmospheric nitrogen fixation by these and other lichen species is desirable because the possibility exists that fixation did occur, but in such small amounts that the fixation was not detected.



College and Department

Plant and Wildlife Sciences



Date Submitted


Document Type





Nitrogen, Fixation; Lichens