PARENT SESSION
Oral Session #4: Plant Ecology: Gas Exchange. Presiding: J. Pereira.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas P&Q.
Drought-imposed limitations on ozone uptake in ponderosa pine forests: measurements and models.
PANEK, JEANNE1, GOLDSTEIN, ALLEN1, KURPIUS, MEREDITH1, 1
ABSTRACT- Tropospheric ozone is a pollutant which is responsible for forest damage worldwide. Ozone must enter foliage through stomatal pores to cause damage. In the seasonally-droughted forests of California and the Pacific Northwest, water limitations can close stomata for long periods of the growing season. Therefore, although ozone concentrations are typically used to assess forest ozone exposure, ozone flux better represents forest ozone exposure here. We are measuring ozone flux to ponderosa pine forests, directly at one site (through eddy covariance methods) and indirectly at 4 sites (from measures of leaf-level stomatal conductance), along an ozone concentration gradient in the Sierra Nevada Mts., CA to develop a model to predict ozone flux based on meteorology. Environmental variables which control stomatal conductance such as soil moisture, atmospheric humidity, solar radiation, and air temperature have been found to influence ozone uptake. Because ponderosa pine forests are water-limited, however, soil moisture and atmospheric humidity were the primary climatic variables which controlled ozone uptake. As soil moisture dropped over time, leaf water potential became increasingly negative and stomatal conductance dropped, constricting ozone flux into the foliage. Although ozone concentrations were higher at the end of the growing season than at the beginning, stomatal conductances and thus ozone fluxes were much smaller, demonstrating a decoupling between ambient ozone concentration and ozone flux. A model has been developed to predict ozone flux from site meteorological variables using these relationships.
KEY WORDS: modeling ozone flux, stomatal conductance, Pinus ponderosa, drought stress