A statistical approach to estimate O-3 uptake of ponderosa pine in a mediterranean climate

In highly polluted sites, stomatal behavior is sluggish with respect to light, vapor pressure deficit, and internal CO2 concentration (G) and poorly described by existing models. Statistical models were developed to estimate stomatal conductance (gs) of 40-year-old ponderosa pine at three sites differing in pollutant exposure for the purpose of calculating O-3 uptake. Gs was estimated using julian day, hour of day, pre-dawn xylem potential and photosynthetic photon flux density (PPFD). The median difference between estimated and observed field gs did not exceed 10 mmol H2O m(-2) s(-1), and estimated gs within 95% confidence intervals. O-3 uptake was calculated from hourly estimated gs, hourly O-3 concentration, and a constant to correct for the difference in diffusivity between water vapor and O-3. The simulation model TREGRO was also used to calculate the cumulative O-3 uptake at all three sites. O-3 uptake estimated by the statistical model was higher than that simulated by TREGRO because gas exchange rates were proportionally higher. O-3 exposure and uptake were significantly correlated (r(2) > 0.92), because O-3 exposure and gs were highly correlated in both statistical and simulation models. (c) 2002 Elsevier Science Ltd. All rights reserved.