Growth responses of yellow-poplar (Liriodendron tulipifera L.) exposed to 5 years of O3 alone or combined with elevated CO2

Abstract

Field-grown yellow-poplar (Liriodendron tulipifera L.) were fumigated from May to October in 1992-96 within open-top chambers to determine the impact of ozone (O3) alone or combined with elevated carbon dioxide (CO2) on sapling growth. Treatments were replicated three times and included: charcoal-filtered air (CF); 1 × ambient ozone (1 × O3); 1.5 × ambient ozone (1.5 × O3); 1.5 × ambient ozone plus 350 p.p.m. carbon dioxide (1.5 × O3 + CO2) (target of 700 p.p.m. CO2); and open-air chamberless plot (OA). After five seasons, the total cumulative O3 exposure (SUM00 = sum of hourly O3 concentrations during the study) ranged from 145 (CF) to 861 (1.5 × O3) p.p.m. × h (parts per million hour). Ozone had no statistically significant effect on yellow-poplar growth or biomass, even though total root biomass was reduced by 13% in the 1.5 × O3-exposed saplings relative to CF controls. Although exposure to 1.5 × O3 + CO2 had a stimulatory effect on yearly basal area growth increment after two seasons, significant increases in shoot and root biomass (∼ 60% increase relative to all others) were not detected until the fifth season. After five seasons, the yearly basal area growth increment of saplings exposed to 1.5 × O3 + CO2-air increased by 41% relative to all others. Based on this multi-year study, it appears that chronic O3 effects on yellow-poplar growth are limited and slow to manifest, and are consistent with previous studies that show yellow-poplar growth is not highly responsive to O3 exposure. In addition, these results show that enriched CO2 may ameliorate the negative effects of elevated O3 on yellow-poplar shoot growth and root biomass under field conditions.