title: Photoprotection, photosynthesis and growth of tropical tree seedlings under near-ambient and strongly reduced solar ultraviolet-B radiation.
abstract: Seedlings of two late-successional tropical rainforest tree species, Tetragastris panamensis (Engler) O. Kuntze and Calophyllum longifolium (Willd.), were field grown for 3-4 months at an open site near Panama City (9 degrees N), Panama, under plastic films that either transmitted or excluded most solar UV-B radiation. Experiments were designed to test whether leaves developing under bright sunlight with strongly reduced UV-B are capable of acclimating to near-ambient UV-B conditions. Leaves of T. panamensis that developed under near-ambient UV-B contained higher amounts of UV-absorbing substances than leaves of seedlings grown under reduced UV-B. Photosynthetic pigment composition, content of alpha-tocopherol, CO(2) assimilation, potential photosystem II (PSII) efficiency (evaluated by F(v)/F(m) ratios) and growth of T. panamensis and C. longifolium did not differ between seedlings developed under near-ambient and reduced solar UV-B. When seedlings were transferred from the reduced UV-B treatment to the near-ambient UV-B treatment, a pronounced inhibition of photosynthetic capacity was observed initially in both species. UV-B-mediated inhibition of photosynthetic capacity nearly fully recovered within 1 week of the transfer in C. longifolium, whereas in T. panamensis an about 35% reduced capacity of CO(2) uptake was maintained. A marked increase in UV-absorbing substances was observed in foliage of transferred T. panamensis seedlings. Both species exhibited enhanced mid-day photoinhibition of PSII immediately after being transferred from the reduced UV-B to the near-ambient UV-B treatment. This effect was fully reversible within 1d in T. panamensis and within a few days in C. longifolium. The data show that leaves of these tropical tree seedlings, when developing in full-spectrum sunlight, are effectively protected against high solar UV-B radiation. In contrast, leaves developing under conditions of low UV-B lacked sufficient UV protection. They experienced a decline in photosynthetic competence when suddenly exposed to near-ambient UV-B levels, but exhibited pronounced acclimative responses.
authors.affiliation: Smithsonian Tropical Research Institute, P.O. Box 0843-03092 Panama, Republic of Panama. ghkrause@uni-duesseldorf.de
authors.forename: G Heinrich
authors.initials: GH
authors.lastname: Krause
authors.forename: Peter
authors.initials: P
authors.lastname: Jahns
authors.forename: Aurelio
authors.initials: A
authors.lastname: Virgo
authors.forename: Milton
authors.initials: M
authors.lastname: García
authors.forename: Jorge
authors.initials: J
authors.lastname: Aranda
authors.forename: Eckard
authors.initials: E
authors.lastname: Wellmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Winter
mesh_terms: D018533:Biomass; D029403:Burseraceae / Q000254:growth & development / Q000528:radiation effects*; D002245:Carbon Dioxide / Q000378:metabolism; D028084:Clusiaceae / Q000254:growth & development / Q000528:radiation effects*; D008027:Light; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000254:growth & development / Q000528:radiation effects; D018517:Plant Roots / Q000254:growth & development / Q000528:radiation effects; D018547:Plant Stems / Q000254:growth & development / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development / Q000528:radiation effects*; D013997:Time Factors; D014197:Trees / Q000254:growth & development / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide