Effects of enhanced UV-B radiation on growth and photosynthetic responses of four species of seedlings in subalpine forests of the eastern Tibet plateau

► Growth, morphological and photosynthetic responses of four species to UV-B. ► Enhanced UV-B reduced total biomass and photosynthesis of the four species. ► Enhanced UV-B caused harmful effects on leaf traits of broad-leaved tree. ► Broad-leaved species are more sensitive to UV-B radiation than conifer species. We assessed the influence of enhanced UV-B radiation on growth, root morphology, leaf morphology and anatomy, pigment concentrations and gas exchange of seedlings of four tree species ( Abies faxoniana, Acer mono, Picea asperata and Swida hemsleyi) from the southeastern Qinghai-Tibetan Plateau of China. Potted seedlings were exposed outdoors in Sichuan Province, China to two levels of UV-B (ambient UV-B, 11.02 KJ m −2 day −1; and enhanced UV-B, 14.33 KJ m −2 day −1). Exposure to enhanced UV-B radiation had significant effects on seedling growth and morphological and photosynthetic traits of the four species. Total and belowground biomass was lower in seedlings exposed to enhanced UV-B radiation in all four species. Concentrations of photosynthetic pigments (Chl (a + b)) and UV-B-absorbing compounds in the leaves of all four species was lower in seedlings exposed to enhanced UV-B radiation, but the Chl a/b ratio was not affected. Enhanced UV-B markedly reduced the net photosynthetic rate and increased the intercellular CO 2 concentration in the four species. Differences in stomatal conductance to water vapor were observed in all four species. Responses differed among the four species. Generally, exposure to enhanced UV-B radiation led to shrinkage and curling of leaves in A. mono and S. hemsleyi seedlings, and reduced the leaf number and mass in A. mono seedlings. Exposure to enhanced UV-B radiation markedly reduced the palisade tissue thickness in A. mono leaves but led to thicker leaves in S. hemsleyi seedlings. These results imply that broad-leaved tree seedlings were more sensitive to enhanced UV-B radiation than conifer seedlings.