Ultraviolet-B radiation effects on early seedling growth of Pinaceae species

Seven coniferous species were grown in the Duke University phytotron under five ultraviolet-B (UV-B = 280–320 nm) radiation regimes for 11 weeks. The irradiation regimes were 765, 680, 637, 310, and 28 mW•m−2 as summed over the 280–320 nm UV-B waveband. The UV-B radiation source was FS40 Westinghouse sunlamps filtered with cellulose acetate for four treatment irradiation levels and clear Mylar for the control. Biomass production of lodgepole pine (Pinuscontorta Dougl.), loblolly pine (Pinustaeda L.), noble fir (Abiesprocera Redh.), ponderosa pine (Pinusponderosa Laws.), and slash pine (Pinuselliottii Engelm.) was significantly reduced at the highest UV-B radiation level and somewhat less at the lower levels. These species were rated as slightly susceptible (5–25% reduction in biomass). Biomass production of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) was unaffected, and white fir (Abiesconcolor (Gord. and Glenn.) Lindl.) biomass was increased significantly by UV-B radiation at 310, 637, and 680 mW•m−2 UV-B radiation levels. Root weight tended to be reduced more than shoot weight, thereby decreasing root:shoot ratios significantly in certain UV-B regimes. Leaf area declined significantly with increasing UV-B radiation for all species except white fir and Douglas-fir. At the higher UV-B irradiance levels, height was significantly reduced when compared with the Mylar control on loblolly, lodgepole, ponderosa, slash pines, and noble fir, respectively. Height of Douglas-fir was not altered and height of white fir was increased significantly at the lowest level of UV-B radiation tested.