Nitrogen fixation in the lichen Lobaria pulmonaria in elevated atmospheric carbon dioxide.

Thalli of Lobaria pulmonaria (L.) Hoffm., a nitrogen-fixing epiphyte common in mesic temperate forests, were collected in a Douglas-fir (Pseudotsuga menziesii Franco) forest near Corvallis, Oregon, and maintained for 20 to 40 days in controlled-environment chambers with atmospheric CO concentrations of 374 and 700 μll. Nitrogenase activity, which was assayed by the acetylene reduction method, was approximately doubled in the lichen maintained in elevated CO. Increases in nitrogen fixation by lichens may be an important part of the integrated ecosystem response to rising CO.