Laboratory UV treatment on field-treated samples
In our study, application of an additional UV treatment to field-treated samples had no significant effect onF v/F m of UV-reduced plants over the 192-hour simulated winter recovery period. This result suggests either that the one year of reduced UV in the field was not sufficient to remove previously acquired acclimation or that these plants may have a physiologically constitutive level of protection in this assay. However, the mechanism of protection in the UV-filtered and UV-transmitted plants might have been different, as there were differences in their pigment and antioxidant profiles. For example, zeaxanthin was higher in UV-filtered plants and zeaxanthin has been found to contribute to UV stress protection and UV damage prevention in tobacco plants (Götz et al. 2002). It is also possible that any PSII damage incurred by the UV treatment was repaired in the 30 minutes dark acclimation period prior to when the first fluorescence measurement was recorded. Curiously, UV-transmitted plants had significantly higherF v/F m at T24 after the laboratory UV treatment, and UV-filtered plants showed the same pattern though it was not significant. This result lends further support to the hypothesis that UV exposure has beneficial effects on photosynthetic efficiency in S. caninervisas even a moderate dose of UV given to desiccated plants resulted in some improvement in F v/F mrecovery.