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

Abstract

The effects of elevated ozone (O₃) levels (80 ppb and 120 ppb) 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 30 days of O₃ fumigation, as well as in control plants; biomass measurements were done only after 30 days 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 (PI_total). The decline of PI_total under the 80 ppb O₃ treatment was due to a lower density of reaction centres (RC/ABS), while the notable decline under the 120 ppb 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 (δ_Ro). Stomatal conductance was affected by both treatments. Biomass was found to be affected by O₃ fumigation (for 30 days), decreasing by 40% at 80 ppb and by more than 70% under 120 ppb. 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 O₃ on biomass of canola plants.

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