Interactive effects of PAR and UV radiation on the physiology, morphology and leaf optical properties of two barley varieties

► Enhanced UV-B significantly reduced the photosynthetic activity of shade acclimated plants. ► Response to UV-B was modified by the leaf age and barley genotype. ► High PAR ameliorated the negative UV effects on photochemistry and CO2 assimilation. ► Accumulation of UV-shielding compounds was induced by high PAR, mainly in young leaves. ► The UV-B effect on plant morphology was modified by PAR.