BROWN, PATRICK J.* AND DAVID A. DALTON. Biology Department, Reed College, Portland, OR 97202. - Nitrogen fixation, photosynthesis, and growth by Lobaria oregana in an old-growth forest canopy.
Lobaria oregana is a nitrogen-fixing cyanolichen that is
spectacularly abundant in old-growth forests of the Pacific Northwest.
This species provides a major source of nitrogen for older forests,
but the ecological factors that determine its distribution are not
well understood. In this study, we used the Wind River Canopy Crane
Research Facility (http://depts.washington.edu/wrccrf/) to study the
physiological activities and growth of transplanted pendants of L.
oregana at 3 positions in the canopy: Top (62 m above the ground),
Middle (39 m), and Bottom (2 m). There was a complex pattern of
seasonal and spatial variation, but in general nitrogen fixation was
greatest at the Middle position and photosynthesis at the Top
position. Greatest growth was found at the Middle position where
there was a 16.4 % increase in dry weight over the 10-month study
period. Lichens at the Bottom position died after transplanting.
Activities were strongly correlated with hydration except that very
high hydration (>200%) inhibited photosynthesis. Laboratory
experiments showed that photosynthesis increased at PPFD's of up to
1000 mmol m-2 sec-1.
This study represents the first attempt to describe how the
physiological activities of L. oregana respond both spatially
and temporally to the extremely variable environment within the
Key words: Lobaria oregana, nitrogen fixation, old-growth forest canopy, photosynthesis