PARENT SESSION
Poster Session #75: Nutrient Cycling II.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC
164
Mapping the abundance and activity of two symbiotic nitrogen fixers in western Oregon.
HICKS, WILLIAM*,1, HARMON, MARK1, OHMANN, JANET2, GREGORY, MATTHEW1, BERRYMAN, SHANTI1, MARTIN, ERIN1, GEISER, LINDA3, 1 Oregon State University, Corvallis, OR2 USDA Forest Service, Corvallis, OR3 USDA Forest Service, Corvallis, OR
ABSTRACT- Nitrogen is an important nutrient regulating plant growth and decomposition, yet accurate regional estimates of biological nitrogen inputs are lacking. In the nitrogen limited forests of western Oregon, Alnus rubra and cyanolichens (primarily Lobaria oregana) are considered to be the two most abundant symbiotic nitrogen fixers. We used regional grids of field plots, mapped environmental data, and regression tree analysis to spatially predict the abundance and distribution of these two N fixers. Previously developed models relating N fixer abundance to annual N fixation rates were used to estimate biological N inputs from these organisms. Alnus rubra basal area and N fixation activity were related to annual temperature variation, deciduous cover, elevation, aspect, disturbance history, latitude, annual precipitation, minimum annual temperature, and distance to the nearest stream (Percent Reduction in Deviance (PRD) = 0.38). For Alnus rubra, the highest basal area (28.7 m2/ha) and N fixation activity (196 kg/ha/yr) occurred in stands with an annual temperature variation < 23.6° C, a deciduous cover > 27%, an elevation < 347 m, a minimum annual temperature < 3.0° C, and a north-facing aspect. Cyanolichen biomass and N fixation activity were related to slope position, elevation, longitude, latitude, aspect, slope, annual temperature variation, distance to nearest stream, and maximum annual temperature (PRD = 0.47). For cyanolichens, the highest biomass (728.5 kg/ha) and N fixation activity (12.6 kg/ha/yr) occurred in stands on the lower quarter of a slope, with elevations < 1046 m, latitudes south of 45.1° north, longitudes west of -122.4°, annual temperature variations < 28.9° C, slopes < 42%, distances to the nearest stream < 25 m, and maximum annual temperatures < 24.5° C. Biological nitrogen inputs from these organisms have a patchy distribution on the landscape.
KEY WORDS: nitrogen, fixation, Alnus, Lobaria