Impact of elevated ozone on chlorophyll a fluorescence in field-grown oat (Avena sativa).

Oat (Avena sativa) plants were grown in the field near the urban area of Valencia, Eastern Spain. The data on air quality showed that ozone was the main phytotoxic pollutant present in ambient air reaching a 7-h mean of 46 nl l(-1) and a maximum hourly peak of 322 nl l(-1). The effect of ambient ozone on PSII activity was examined by measurements of chlorophyll (Chl) a fluorescence. In leaves with visible symptoms, the function of PSII was changed at high actinic irradiances. Nonphotochemical quenching (NPQ) was higher and quantum efficiency of PSII (Phi(PSII)), photochemical quenching (q(p)), quantum efficiency of excitation capture and PSII electron flow (F(v)'/F(m)') were lower. An enhanced susceptibility to photoinhibition was observed for symptom-exhibiting leaves compared to leaves that remain free of visible symptoms. Both the lowering of photosynthesis efficiency and the increased sensitivity to photoinhibition probably contribute to reduced crop yield in the field, to different extents, depending on growth conditions. To our knowledge, this is the first report that demonstrates that quantum efficiency of exciton trapping in PSII is associated with foliar injury in oat leaves in response to ambient concentration of ozone.