diurnal course; growth chambers; photosynthetic pigments composition; Picea abies; reflectance continuum removal; xanthophyll cycle

The experiment tested the ability of the spectral index called ?area under curve normalised to maximal band depth? (ANMB) to track dynamic changes in the xanthophyll cycle of Norway spruce needles. Spruce seedlings were gradually acclimated to different PPFDs and air temperature regimes. A significant decline in the chlorophylls to carotenoids ratio and the increase of the amount of xanthophyll cycle pigments indicated a higher need for carotenoid-mediated photoprotection in spruce acclimated to high PPFD. Similarly, the photochemical reflectance index (PRI) changed from positive to negative values after changing light conditions from low to high intensity. Systematic responses of PRI to DEPS were, however, observed only during high temperature treatments and after the exposition of needles to high irradiance. The ANMB index computed from needle reflectance was able to track dynamic changes in DEPS without any influence induced by changing the content of leaf photosynthetic pigments.