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Interactions between Acclimation and Photoinhibition of Photosynthesis of a Tropical Forest Understorey Herb, Alocasia macrorrhiza, during Simulated Canopy Gap Formation
S. S. Mulkey and R. W. Pearcy
Vol. 6, No. 6 (1992), pp. 719-729
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2389969
Page Count: 11
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1. The effects of a sudden increase in irradiance and the high leaf temperatures characteristic of a canopy gap environment were studied with chlorophyll fluorescence and gas-exchange measurements on shade- and sun-acclimated leaves of Alocasia macrorrhiza. 2. Photoinhibition occurred in both sun and shade leaves during a 2-h simulated gap treatment (1900 μ mol photons m-2 s-1) in which leaf temperatures rose to 40⚬C. Dissipation of excess energy was more efficient in sun leaves, which showed rapid quenching of fluorescence. The quantum yield of photosystem II as calculated from fluorescence in low light was considerably lower for shade than sun leaves after the gap treatment. 3. Fluorescence relaxation kinetics showed that sun leaves recovered overnight from photoinhibition even when leaf temperatures during treatment reached 40⚬C. By contrast, shade leaves given the same treatment had not recovered after 4 days in low light. Shade leaves given the same light treatment but held at 30⚬C instead of 40⚬C recovered within 4 days. Shade leaves treated at 40⚬C in moderate, saturating light (375 μ mol photons m-2 s-1) recovered overnight. Thirteen days of 3-h gap treatments on whole plants previously grown in shade showed that after initial depressions both fluorescence and photosynthetic capacity partially recovered. 4. Thus, the degree of photoinhibition and the potential for recovery are dependent on the synergistic roles of leaf temperatures and high light during initial gap conditions. Although quantum efficiency and photosynthetic capacity can be impaired by strong light and heat stress, shade leaves have significant capacity for repair and contribution to the whole-plant carbon budget during acclimation following gap formation.
Functional Ecology © 1992 British Ecological Society