Violaxanthin cycle pigment de-epoxidation and thermal dissipation of light energy in three boreal species of evergreen conifer plants

We studied carotenoid composition and chlorophyll fluorescence in two-year-old needles from Siberian spruce (Picea obovata (L.) Karst.), Siberian fir (Abies sibirica L.), and common juniper (Juniperus communis L.). The highest values of maximum PSII photochemical activity (F _v/F _m) equaling 0.82–0.85 were observed in July–September. The decrease in F _v/F _m in December–March was more pronounced in juniper (down to 0.15) than in spruce and fir (0.45–0.50). In May, we observed a nearly complete recovery in maximum PSII photochemical activity in fir and spruce (0.72–0.77), while in juniper, the F _v/F _m value was notably lower (0.65–0.67). The amount of thermal dissipation of energy absorbed by PSII LHC did not exceed 30% in summer and equaled 60–90% in winter and early spring. The carotenoid pool consisted mainly of xanthophylls, among which lutein (70%), neoxanthin (7–10%), and a violaxanthin cycle (VXC) component — violaxanthin (3–15%) were constantly present. The accumulation of two other VXC pigments—zeaxanthin and antheraxanthin, was noted in December–March. In July, these xanthophylls were not identified. We discovered a direct connection between VXC pigment de-epoxidation level and light energy thermal dissipation in boreal conifer leaves. Such association reflects the non-species-specific character of the mechanism for quenching zeaxanthin-dependent nonphotochemical chlorophyll fluorescence in PSII LHC in winter and spring.