Effects of enhanced UV-B radiation on six north temperate forest tree species with contrasting leaf anatomy.
Bassman1, J.H., G.E. Edwards2, and R. Robberecht3. 2000.

Workshop on Impacts of UV Radiation on Terrestrial and Aquatic Ecosystems. Abstract. 2nd SPARC General Assembly, Stratospheric Processes and their Role in Climate, World Climate Research Programme, November 6 - 10, 2000, Mar del Plata, Argentina.

Seeds or cuttings of six forest tree species with contrasting leaf anatomies and shoot growth characteristics were cultivated under three different UV-B radiation regimes: ambient (7.5 kJ m-2 d-1 = 1X), two times ambient (2X), or three times ambient (3X) biologically effective UV-B radiation (UV-BBE) as calculated for Pullman, Washington, USA at the summer solstice. Net photosynthesis (Pn) increased in developing leaves, was unaffected in recently mature leaves, and decreased in older leaves in Populus deltoides under 2X and 3X treatments compared to 1X plants.  Pn was reduced by 2X and 3X treatments in Populus trichocarpa, and by the 3X regime for Pseudotsuga menziesii.  Pn increased under the 2X treatment for P. menziesii and the 3X treatment for Picea engelmannii.  For Pinus ponderosa and Quercus rubra, Pn was unchanged.  Dark respiration increased under both 2X and 3X treatments for P. engelmannii and by the 3X level in Q. rubra, but was unaffected in the other species.   Transpiration and stomatal conductance generally mirrored changes in photosynthesis.  Water use efficiency increased for P. ponderosa (2X treatment) and Q. rubra (2X & 3X), was reduced for P. trichocarpa (2X & 3X), and remained unchanged in the other species.  Enhanced UV-B radiation changed the shape of light response curves for all species.  Quantum yields were unchanged for P. ponderosa but increased for P. menziesii (2X) and P. engelmannii (2X & 3X).  Light compensation points were higher in the conifers (3X) and reduced in the angiosperms (2X).  Chlorophylls were generally reduced by higher UV-B radiation in the conifers and for P. trichocarpa (3X), but increased for Q. rubra.  UV-absorbing compounds increased in the conifers, were unchanged in P. trichocarpa and Q. rubra, and reduced in P. deltoides (3X) by enhanced UV-B radiation. Height growth increased (P. ponderosa, 3X; Q. rubra, 2X), decreased (P. engelmannii, 3X; P. deltoides, 2X & 3X) or was unchanged (P. menziesii, P. trichocarpa) by higher levels of UV-B radiation.  Stem diameter and plant biomass were generally reduced, and shoot:root ratios increased for all species except P. trichocarpa. Results do not appear to support the hypothesis that inherent leaf anatomy or shoot growth pattern in these species directly determine the response of photosynthesis and growth to enhanced UV-B radiation.


1 Department of Natural Resource Sciences, Washington State University, Pullman WA  99164-6410, USA

2 Department of Botany, Washington State University, Pullman WA  99164-4238, USA

3 Department of Rangeland Ecology, University of Idaho, Moscow, ID  83844-1135, USA