EVIDENCE THAT OZONE EXPOSURE INCREASES THE SUSCEPTIBILITY OF PLANTS TO NATURAL FROSTING EPISODES

This study investigates the phytotoxicity of ozone during periods of n atural frosts following long-term fumigation. Heather (Calluna vulgari s (L.) Hull.) plants were fumigated with ozone for 6 months at 70 nl l (-1), for 8 h d(-1), 5 d a week in open-top chambers. Natural frosting occurred within the chambers towards the end of this period (5-27 Dec ember 1995). Plant responses to the ozone/natural frosting episode wer e recorded in January 1996. We show conclusively that naturally occurr ing frost exposure results in increased damage and mortality for ozone -treated plants, which could have important implications for the funct ion of heathland ecosystems.