The effects of UV-B radiation on epidermal anatomy in loblolly pine (Pinustaeda L.) and Scots pine (Pinus sylvestris L.)

The effects of enhanced UV-B radiation on the needle anatomy of loblolly pi ne (Pinus taeda L.) and Scots pine (Pinus sylvestris L.) were studied in th e field under supplemental UV-B radiation supplied by a modulated irradiati on system. The supplemental UV-B levels were designed to simulate either a 16 or 25% loss of stratospheric ozone over College Park, Maryland. Enhanced UV-B radiation caused different responses in these two species. The needle s of loblolly pine had larger amounts of tannin in the lumen of epidermal c ells and more wall-bound phenolics in the outer epidermal walls of UV-B-tre ated needles, whereas the most pronounced effect on Scots pine needles was increased cutinization. In both species, the outer epidermal cell walls thi ckened and the needle cross-sectional and mesophyll areas decreased (statis tically significantly only in Scots pine). This suggests that more carbon m ay have been allocated to the protection mechanisms at the expense of photo synthetic area. The difference in response between these species suggests t hat the response to UV-B radiation is not mediated by a single mechanism an d that no generalization with regard to the effects of UV-B on conifers can be made.