Effects of pre-exposure to ultraviolet-B radiation on responses of tomato ( Lycopersicon esculentum cv. New Yorker) to ozone in ambient and elevated carbon dioxide

“Capsule”: Pre-exposure to enhanced UV-B mitigated ozone damage to leaf photosynthesis at elevated carbon dioxide concentrations. Patterns of environmental change in the biosphere include concurrent and sequential combinations of increasing ultraviolet (UV-B) and ozone (O 3) at increasing carbon dioxide (CO 2) levels; long-term changes are resulting mainly from stratospheric O 3 depletion, greater tropospheric O 3 photochemical synthesis, and increasing CO 2 emissions. Effects of selected combinations were evaluated in tomato ( Lycopersicon esculentum cv. New Yorker) seedlings using sequential exposures to enhanced UV-B radiation and O 3 in differential CO 2 concentrations. Ambient (7.2 kJ m −2 day −1) or enhanced (13.1 kJ m −2 day −1) UV-B fluences and ambient (380 μl l −1) or elevated (600 μl l −1) CO 2 were imposed for 19 days before exposure to 3-day simulated O 3 episodes with peak concentrations of 0.00, 0.08, 0.16 or 0.24 μl l −1 O 3 in ambient or elevated CO 2. CO 2 enrichment increased dry mass, leaf area, specific leaf weight, chlorophyll concentration and UV-absorbing compounds per unit leaf area. Exposure to enhanced UV-B increased leaf chlorophyll and UV-absorbing compounds but decreased leaf area and root/shoot ratio. O 3 exposure generally inhibited growth and leaf photosynthesis and did not affect UV-absorbing compounds. The highest dose of O 3 eliminated the stimulating effect of CO 2 enrichment after ambient UV-B pre-exposure on leaf photosynthesis. Pre-exposure to enhanced UV-B mitigated O 3 damage to leaf photosynthesis at elevated CO 2.