Seedling growth and leaf surface morphological responses of three rangeland weeds to ultraviolet-B radiation

Abstract

The influence of ultraviolet-B (UV-B) radiation on seedling growth and leaf surface characteristics of important rangeland weedsCynoglossum officinaleL. (houndstongue),Centaurea diffusaLam. (diffuse knapweed), andTragopogon pratensisL. (meadow salsify) was investigated in a greenhouse by exposing seedlings to 0, 7, or 11 kJ m−2d−1of biologically effective UV-B radiation. UV-B radiation reduced leaf, stem, and root fresh weights, leaf area, and leaf: shoot ratio and increased shoot dry matter content, specific leaf weight, and leaf greenness ofC. officinaleseedlings. Leaf, stem, and root fresh weight, and leaf area ofC. diffusaseedlings decreased, whereas shoot dry matter content, specific leaf weight, leaf: shoot ratio, and leaf greenness were unaffected.T. pratensisseedlings exposed to UV-B radiation had diminished leaf greenness, but no change was observed in leaf or stem fresh weight, leaf area, or leaf: shoot ratio. Uniseriate trichome abundance inC. officinaleseedlings increased and trichome orientation changed in response to UV-B exposure. UV-B treatments decreased uniseriate trichome abundance inC. diffusa; glandular trichome abundance and the ratio of glandular: uniseriate trichomes were not affected.T. pratensisseedlings showed no change in the amount of epicuticular wax on the adaxial leaf surface in response to UV-B irradiation. Shoot dry weight was not influenced by removal of epicuticular wax prior to UV-B exposure. Results suggest that epicuticular wax is not an important factor in acclimation ofT. pratensisseedlings to UV-B radiation. Susceptibility to UV-B–induced damage was greatest forC. officinaleseedlings and least forT. pratensisseedlings. Modification of plant morphology or reduction in growth induced by enhanced UV-B radiation may influence competitive relationships between rangeland weeds and their associated forage species.