title: Photosynthesis, photoprotection, and growth of shade-tolerant tropical tree seedlings under full sunlight.
abstract: High solar radiation in the tropics is known to cause transient reduction in photosystem II (PSII) efficiency and CO(2) assimilation in sun-exposed leaves, but little is known how these responses affect the actual growth performance of tropical plants. The present study addresses this question. Seedlings of five woody neotropical forest species were cultivated under full sunlight and shaded conditions. In full sunlight, strong photoinhibition of PSII at midday was documented for the late-successional tree species Ormosia macrocalyx and Tetragastris panamensis and the understory/forest gap species, Piper reticulatum. In leaves of O. macrocalyx, PSII inhibition was accompanied by substantial midday depression of net CO(2) assimilation. Leaves of all species had increased pools of violaxanthin-cycle pigments. Other features of photoacclimation, such as increased Chl a/b ratio and contents of lutein, β-carotene and tocopherol varied. High light caused strong increase of tocopherol in leaves of T. panamensis and another late-successional species, Virola surinamensis. O. macrocalyx had low contents of tocopherol and UV-absorbing substances. Under full sunlight, biomass accumulation was not reduced in seedlings of T. panamensis, P. reticulatum, and V. surinamensis, but O. macrocalyx exhibited substantial growth inhibition. In the highly shade-tolerant understory species Psychotria marginata, full sunlight caused strongly reduced growth of most individuals. However, some plants showed relatively high growth rates under full sun approaching those of seedlings at 40 % ambient irradiance. It is concluded that shade-tolerant tropical tree seedlings can achieve efficient photoacclimation and high growth rates in full sunlight.
authors.affiliation: Smithsonian Tropical Research Institute, Apartado Postal, 0843-03092, Panama, Republic of Panama. ghkrause@uni-duesseldorf.de
authors.forename: G Heinrich
authors.initials: GH
authors.lastname: Krause
authors.forename: Klaus
authors.initials: K
authors.lastname: Winter
authors.forename: Shizue
authors.initials: S
authors.lastname: Matsubara
authors.forename: Barbara
authors.initials: B
authors.lastname: Krause
authors.forename: Peter
authors.initials: P
authors.lastname: Jahns
authors.forename: Aurelio
authors.initials: A
authors.lastname: Virgo
authors.forename: Jorge
authors.initials: J
authors.lastname: Aranda
authors.forename: Milton
authors.initials: M
authors.lastname: García
mesh_terms: D000042:Absorption / Q000528:radiation effects; D000222:Adaptation, Physiological / Q000528:radiation effects*; D002245:Carbon Dioxide / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development* / Q000528:radiation effects*; D013472:Sunlight; D024505:Tocopherols / Q000378:metabolism; D014197:Trees / Q000254:growth & development* / Q000528:radiation effects*; D014329:Tropical Climate; D014466:Ultraviolet Rays
chemical_list: D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D024505:Tocopherols