PARENT SESSION
Oral Session #31: Plant Ecology: Gas Exchange.
Presiding: R. Montgomery
Tuesday, August 6. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Environmental control of stomatal behavior: PPFR, VPD, and ... [O₃]?

Grulke, Nancy^*,1, ¹ USDA Forest Service, Riverside, CA

ABSTRACT- There is no one model that fully explains stomatal behavior. Substomatal CO₂ concentration, absolute humidity or VPD, PPFR, T_L, pre-dawn , and physiological constraints all have been used to explain stomatal behavior. At low O₃ exposure levels, the models and field data support a proportional change in gs with assimilation. At higher O₃ exposures, there are irregularities in stomatal behavior. Gs of ponderosa pine at 5 min intervals was statistically predicted at a moderate O₃ exposure site, allowing the model to choose the best environmental variates. Under non-drought conditions, short and season-long O₃ exposure metrics were significant variates with T_L, VPD, and PPFR. Under drought conditions, medium-term O₃ exposure metrics were significant variates with VPD, PPFR and predawn . Under steady PPFR, seasonal O₃ exposure was a significant variate, but under fluctuating light, both short and medium term O₃ exposure metrics were significant variates. Previous hour O₃ concentration was a significant variate in predicting gs at dawn. O₃ metrics were statistically significant, persistant environmental variates in predicting gs. Moderate O₃ exposures are common in half of the Sierra Nevada in a typical year, and in up to one third of the continental US under dry, warm conditions in the summer. O₃ exposure may be a significant, but rarely identified environmental factor influencing stomatal behavior in ecological studies.

KEY WORDS: stomatal behavior, O₃ exposure, fluctuating light, ponderosa pine