GROWTH AND FRUITING OF TOMATO AS INFLUENCED BY ELEVATED CARBON-DIOXIDE AND OZONE

'Tiny Tim' tomato plants were exposed to five CO2 treatments (375 (amb ient), 450, 525, 600 or 675 mu mol mol(-1)) in combination with O-3 (O or 80 nmol mol(-1)). Biomass was evaluated following 3, 5, 7 and 13 w k exposure. Biomass following 13 wk exposure also included weekly harv ests of mature tomato fruit beginning week 8. Carbon dioxide enrichmen t significantly enhanced total vegetative plant d. wt at each harvest, as well as cumulative yield of mature fruit, whereas O-3 significantl y suppressed total Vegetative plant d. wt at each harvest and reduced total cumulative fruit yield. The magnitude of these changes varied wi th the development of tomato from early growth to mature fruit yield. Carbon dioxide enrichment reduced the detrimental effects of O-3 on to tal vegetative plant d. wt of tomato following 3, 5, 7 and 13 wk expos ure. Final mature fruit yield was 24% higher under enriched CO2 treatm ents than in ambient CO2. Ozone suppressed final yield by 31% followin g exposure to 80 nmol mol(-1) O-3 when compared with exposure to charc oal-filtered (CF) air. The impacts of both CO2 and O-3 on yield were, however, dependent upon the presence or absence of the other gas. In t he absence of O-3, yields were very similar for the ambient and elevat ed CO2 treatments, but in the presence of O-3, yields under ambient CO 2 were greatly suppressed whereas yields under elevated CO2 were simil ar to those in the absence of O-3. Thus, enriched CO2 ameliorated most of the suppressive effect of O-3 on yield of mature fruit.