The Influence of Environmental Factors on the Sensitivity of Virginia Pine to Ozone

Virginia pine seedlings were injured more severely when exposed to 25 pphm O3 for 4 hr at high humidities than when exposed to this dose at low humidities. The percent relative humidity at which plants were maintained before or after exposure did not affect the amount of injury. In contrast, a direct correlation was observed between the temperature at which plants were maintained before and after exposure and the amount of O/sub 3/ injury. Seedlings kept in the light for 24 hr or longer prior to exposure were protected from injury. Plants maintained in darkness for periods up to 96 hr before exposure were injured. Postexposure extended light periods did not affect symptom development; however, extended dark periods following exposure delayed typical symptom development until the seedlings were placed in the light. 15 references, 5 figure