The Use of OJIP Fluorescence Transients to Monitor the Effect of Elevated Ozone on Biomass of Canola Plants

The effects of elevated ozone (O-3) levels (80ppb and 120ppb) on photosynthetic efficiency and growth of canola plants were studied in open-top chambers. The chlorophyll a polyphasic fluorescence rise kinetics OJIP, stomatal conductance and Chlorophyll Content Index (CCI) were measured after 15 and 30days of O-3 fumigation, as well as in control plants; biomass measurements were done only after 30days with and without fumigation. Analysis of the OJIP kinetics by the JIP-test led to the calculation of several photosynthetic parameters and the total Performance Index (PItotal). The decline of PItotal under the 80ppb O-3 treatment was due to a lower density of reaction centres (RC/ABS), while the notable decline under the 120ppb treatment was found to be due both to a further decline of RC/ABS and to a pronounced lowering of the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end acceptors ((Ro)). Stomatal conductance was affected by both treatments. Biomass was found to be affected by O-3 fumigation (for 30days), decreasing by 40% at 80ppb and by more than 70% under 120ppb. Our findings indicate that biomass decline is due both to the lowering of CCI and the lowering of photosynthetic efficiency parameters. They thus suggest that two simple, non-invasive and rapid methods, namely, the analysis of OJIP fluorescence transients and the measurement of CCI, can be used to screen the effect of elevated O-3 on biomass of canola plants.