PARENT SESSION
Oral Session 1: Aquatic Ecology I: Rivers, Nutrients, and Water Quality.
Presiding: D Kashian
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 105.
Stoichiometry of Rio Grande cottonwoods in response to natural and anthropogenic nutrient addition.
Harner, Mary*,1, Tibbets, Teresa1, 1 The University of New Mexico, Albuquerque, NM, USA
ABSTRACT- Cottonwood trees dominate many floodplain forests and play a substantial role in the cycling of nutrients in riparian ecosystems. However, the effect of nutrient subsidies from natural and anthropogenic sources on cottonwood leaf tissue C:N:P is poorly understood. We studied leaf C:N:P of cottonwoods (Populus deltoides ssp. wislizenii) in relation to nutrient inputs from natural (flooding and fire) and anthropogenic (waste-water effluent) sources along the Rio Grande in central New Mexico. We also conducted greenhouse experiments where we fertilized cottonwoods with nitrogen and phosphorus and measured leaf C:N:P. Flooding was minimal during the study, but at two sites that historically received over-bank flooding, leaf N:P was lower compared to leaves from other study sites. Cottonwoods growing above groundwater flow paths that originate near a large waste-water treatment facility had higher leaf % N compared to other cottonwoods. At two study sites that experienced fire, leaves of sucker cottonwoods had higher % N and % P and lower leaf N:P compared to trees before the fire, and the suckers produced litter with lower C:N compared to trees from unburned sites. In greenhouses, cottonwoods that received nitrogen additions had higher % N, lower % P, higher N:P, and similar C:N compared to untreated trees or trees fertilized with P. Our analyses indicate that cottonwoods have variable responses to nutrients during the growing season, but fertilized trees produce litter with higher concentrations of nutrients. These increases in litter quality following nutrient addition may affect decomposition rates and the cycling of nutrients in river ecosystems.
Key words: stoichiometry, Populus, nutrient