Ozone-induced changes in CO 2 assimilation, O 2 evolution and chlorophyll a fluorescence transients in barley

Abstract

Spring barley ( Hordeum vulgare cv. Klaxon) plants, 9 days old, were exposed to 0.05, 0.10 or 0.15 μl litre −1 ozone (O 3) for 12 days. Fumigation was administered for 7 h between 9.00 h and 16.00 h each day. Using conventional IRGA equipment, the carbon dioxide exchange rate (CER) was shown to decrease with increasing concentration of O 3 during the exposure period, falling to 60% of the control value at the highest O 3 concentration. Transpiration rates and stomatal conductance showed similar trends. Light saturation curves, obtained using a leaf disc oxygen electrode, demonstrated that O 3-treated leaves had lower apparent quantum yields (QY) and generally lower rates of O 2 evolution at saturating light and CO 2 levels. Oscillations in chlorophyll a fluorescence, normally observed in control plants, could not be detected after O 3 treatment and could only be restored to some extent by feeding the phosphate sequestering agent d-mannose to the leaves.