A flux-based assessment of the effects of ozone on foliar injury, photosynthesis, and yield of bean (Phaseolus vulgaris L. cv. Borlotto Nano Lingua di Fuoco) in open-top chambers

Open-Top Chamber (OTC) experiments on Phaseolus vulgaris were conducted in summer 2006, to study the ozone effects on visible and invisible leaf injury, photosynthetic efficiency and plant productivity. A Jarvisian stomatal conductance model was drawn up and parameterized allowing the calculation of stomatal ozone uptake in filtered and non filtered OTCs. A multidisciplinary approach was employed to evaluate the ozone effects on plants including: chlorophyll fluorescence and reflectance measurements, histo-cytochemical analyses and yield analysis. The results showed that microscopical leaf symptoms preceded by 3-4 days the appearance of visible symptoms and were strictly correlated with ozone stomatal uptake Stomatal flux critical level for visible leaf injury onset was found around 1.33 mmol O3 m-2. Significant linear dose-response relationships were obtained between cumulative ozone stomatal flux and optical indices (i.e. PRI, NDI and ΔF/Fm ). The negative ozone effects on photosynthesis inevitably reduced plant productivity, affecting the number of pods and seeds, but not seed weight. These results, besides contributing to the development of a flux-based ozone risk assessment for crops in Europe point out the great potentiality of spectral reflectance in evaluating photosynthetic activity reduction in crops.