The effect of long-term ozone fumigation on the growth, physiology and frost sensitivity of Calluna vulgaris

Calluna vulgaris (L) Hull. plants were fumigated in open-top chambers with ambient charcoal-filtered air, or 70 nl l(-1) (70 ppb) ozone, for 8 h a day, five days a week. Ozone treatment during the winter increased the frost sensitivity of plants as measured by electrolyte leakage following a controlled frosting regime. Root growth was decreased and the allometric root:shoot ratio (k) was reduced by the ozone treatment, reflecting a decrease in the partitioning of carbon to the roots. There was no significant effect of ozone on instantaneous net photosynthesis. There was a significant increase in anthocyanin content in ozone;fumigated plants, but no effect on chlorophyll content. In contrast with the effects of wintertime exposure, plants treated during summer showed no significant responses. These results suggest that Calluna vulgaris can be adversely affected by prolonged ozone episodes in the field, particularly if these are followed by or coincide with frosting temperatures.