The effects of possible ambient concentrations of SO2 and O3 on biomass production and gas exchange of radish (Raphanus sativus L, cv. Cherry Belle) are examined, the relationship between photosynthesis and growth is defined and the mechanisms behind pollutant induced changes in growth are elucidated.
Ozone was shown to be considerably more phytotoxic than SO2. Fumigation at a concentration as low as 5 μmol O3 m−3 (0.12μl 1−1) produced ‘visible’ injury. No ‘visible’ injury symptoms were apparent with plants fumigated with SO2. The effect of fumigation with Oa at concentrations greater than 2.5 μmol m−3 (0.06 μl 1−1) was to reduce biomass production and alter carbon partitioning. This was not so for SO2, fumigated plants. Ozone-fumigated plants showed a significant reduction in their photosynthetic efficiency (NAR) and despite an increase in LAR, RGR was still depressed below control values.
The relationship between photosynthesis and biomass production for fumigated plants was examined and whole plant carbon acquisition was calculated from gas-exchange measurements. On comparing calculated carbohydrate production with measured biomass accumulation, it was dear that changes in A were closely related to changes in growth.
Light- and CO2-response curves were used to determine maximum light-saturated photosynthesis (Amax), incident quantum yield (QY) and carboxylation efficiency (d.A/de1), RuBP-regeneration capacity (Jmax) respectively. The presence of SO2 over a concentration of 2.5–8.3 μmol m−3 (0.12–0.20 μl −1) enhanced Amax. QY and Jmax, However, dA/dc1, was reduced at all concentrations. This reduction was offset by an increase in Jmax. At the smallest O3 concentration (2.5 μmol m−3) Amax was stimulated and at the higher concentration severely reduced. Q Y was not negatively influenced by the presence of O3, but d.A/dc1 and Jmax were reduced, particularly as the dose increased.