Lobaria oregana is a nitrogen-fixing cephalodiate lichen that is abundant in old-growth forests west of the Cascades. Although this lichen is believed to be an important source of nitrogen input to the old-growth ecosystem, few studies have measured in situ rates of nitrogen-fixation for Lobaria oregana. In this project, we are using the Wind River Canopy Crane Research Facility to sample Lobaria oregana thalli growing in the canopy, thereby measuring and linking instantaneous rates of nitrogen-fixation, photosynthesis, and water content. We will assess these physiological processes at regular intervals throughout the year. Additional samples are collected and brought back to the lab for analysis of thallus nitrogen content, and for rehydration experiments to determine the lichen's capacity for recovering metabolism following desiccation. We are using the Acetylene Reduction Assay as a surrogate measurement of nitrogen-fixation capacity, and net photosynthesis is measured with a Li-Cor 6400 Portable Photosynthetic Meter. Initial measurements made in December, 1999 indicated levels of nitrogen-fixation and photosynthesis for Lobaria oregana that were below detectable thresholds. Using the physiological data derived from this project, meteorological data from the WRCCRF, and lichen biomass data available from earlier studies, we will determine seasonal trends of metabolic activity in Lobaria oregana, and estimate its potential contribution of fixed nitrogen to the forest.

Key words: cephalodiate lichen, Lobaria oregana, nitrogen fixation, Wind River Canopy Crane Research Facility