EFFECTS OF OZONE ON WHITE CLOVER - PROTECTION OF OZONE DAMAGE BY ETHYLENEDIUREA

The antiozonant ethylenediurea N-[2(2-oxo-1-imidazolidinyl)-ethyl]-N'- phenylurea; EDU) has been reported to protect plants against injury in duced by ozone (O-3). An O-3-sensitive white clover cultivar (Trifoliu m repens cv. Karina) was exposed in open-top chambers ventilated with charcoal-filtered (CF) air or CF to which approximately 60 ppb O-3 (8- h seasonal mean) was added. In each chamber, one-half of the plants wa s treated with EDU as a soil drench to determine effects of O-3 and ED U on plant growth as well as on response variables (leaf gas exchange, superoxide dismutase, soil microbial activity) that have been propose d to be involved in the protective action of EDU against O-3 injury. O -3 exposure resulted in foliar injury and premature senescence, reduct ions in root and shoot growth, and decreases in foliar chlorophyll con centration. The O-3-induced leaf damage and earlier senescence was alm ost completely protected by EDU treatment. EDU did significantly alter root growth but suppressed the O-3-induced shoot reduction. No signif icant effects of EDU were found on leaf transpiration and stomatal res istance, superoxide dismutase activity, or soil microbial C (Cmic), in dicating that stomatal responses, superoxide dismutase, and edaphic fa ctors are not directly involved in the mode of EDU action.