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

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 CO2 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.

► 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.