The experimental material consisted of leaves obtained from 6- and 2-year-old alfalfa plants. Samples were obtained from a field experiment. One day prior to sowing, seeds were stimulated using He-Ne laser light with a surface power density of 6 mW∙cm⁻² – free-fall exposure (L) repeated three times; alternating magnetic field with 30 mT induction and 30 s (P) exposure time; and a combination of laser light and magnetic field (L+P). The results of the stimulation treatments were referenced to non-stimulated samples (control – K). The obtained values of fluorescence lifetime varied from 8.98 to 12.90 ns (t1) and from 3.84 to 5.14 ns (t2). The physical factors applied caused an extension of the lifetimes (t1 and t2), as well as an increase in the chlorophyll a and carotenoid content in 6-year-old cv. Radius leaves, as compared to the control. Contrary observations (i.e., a decrease in the aforementioned indicators) were made for cv. Ulstar (old). In the case of magnetic field stimulation, the longest fluorescence lifetimes, the highest concentrations of chlorophyll a and carotenoids were noted for cv. Radius (old). The content of chlorophyll a was significantly higher in young Lucerne than in older plants.
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