Nitrogen fixation by Stereocaulon paschale under field conditions

Abstract

Nitrogen fixation (C2H2 reduction) by the lichen Stereocaulon paschale (L.) Fr. was studied in the field in northern Sweden. Field studies were carried out in a very dry dwarf-shrub-type pine forest with S. paschale as the only nitrogen-fixing lichen species. During May–September 1973 and 1974 nitrogen fixation was measured on 28 occasions at irregular intervals, and a total of about 1200 lichen samples were studied. The mean nitrogen-fixation activity during May–September was 0.85 and 1.04 μg N g−1 dry weight h−1 for 1973 and 1974 respectively. The water content of the thallus was the most important factor influencing the nitrogen-fixation activity. Studies on gain and loss of thallus water served as a basis for calculating the number of hours when nitrogen fixation occurred. In the area investigated, with S. paschale covering 14% of the ground, the species was calculated to contribute 0.1 g nitrogen fixed per square metre during May–September 1974.