High-light stress does not impair biomass accumulation of sun-acclimated tropical tree seedlings (Calophyllum longifolium Willd. and Tectona grandis L. f.).
Studies with seedlings of tropical rainforest trees ( Calophyllum longifolium Willd.; Tectona grandis L. f.) were designed to test whether high-light stress affects photosynthetic performance and growth. Seedlings were cultivated in pots at a field site in Central Panama (9 degrees N) and separated into two groups: (1) plants exposed to full solar radiation; (2) plants subjected to automatic neutral shading (48 %) whenever visible irradiance surpassed 1000, 1200, or 1600 micromol photons m-2 s-1. After 2-4 months, chlorophyll fluorescence (Fv/Fm ratio), photosynthetic net CO2 uptake, pigment composition, alpha-tocopherol content of leaves, and plant biomass accumulation were measured. Fully sun-exposed, compared to periodically shaded plants, experienced substantial high-light stress around midday, indicated by photoinhibition of photosystem II and depressed net CO2 uptake. Higher contents of xanthophyll cycle pigments, lutein, and alpha-tocopherol showed an enhancement of photoprotection in fully sun-exposed plants. However, in all experiments, the maximum capacity of net CO2 uptake and plant dry mass did not differ significantly between the two treatments. Thus, in these experiments, high-light stress did not impair productivity of the seedlings studied. Obviously, the continuously sun-exposed plants were capable of fully compensating for any potential costs associated with photoinhibition and repair of photosystem II, reduced CO2 assimilation, and processes of high-light acclimation.
Krause
G H
GH
Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Panama. ghkrause@uni-duesseldorf.de
Gallé
A
A
Virgo
A
A
García
M
M
Bucic
P
P
Jahns
P
P
Winter
K
K
D000064:Acclimatization; D018533:Biomass; D029759:Calophyllum / Q000254:growth & development*; D002245:Carbon Dioxide / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development*; D013472:Sunlight; D013696:Temperature; D014197:Trees / Q000254:growth & development*; D014329:Tropical Climate; D029648:Verbenaceae / Q000254:growth & development*
D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide