How photosynthetic light phase of spiny cocklebur (Xanthium spinosum L.) changes during times after herbicide application?

The photosynthetic light phase of spiny cocklebur (Xanthium spinosum L.) plant was studied by JIP-test at different times (12, 36, 60 and 84 hours) after the application of nicosulfuron (®Cruz) and bentazon (®Basagran) herbicides. Results indicated that the application of nicosulfuron did not affect most of the chlorophyll a fluorescence (ChlF) parameters. But, the application of bentazon significantly decreased PSII activity due to increasing F0 and decreasing Fm, Fv, Fv/F0 and especially Fv/Fm. The maximum effect of bentazon was observed on the donor side of PSII by increasing ABS/RC and decreasing TRo/RC and also by reduction of φE0. Reduction in photosynthesis relative vitality (PI) of photosynthesis apparatus by bentazon affected photosystem II (PSII) reaction centers, Fv/Fm and φE0. The highest negative effect of bentazon on PSII activity was recorded at 36 hours after herbicide application. Bentazon via increasing KP, decreased electron transportation.