Twenty-two common British angiosperms were examined for their ability to acclimate photosynthetically to sun and shade conditions. Plants were grown under low irradiance, far-red enriched light (50 μmol m−2 s−1), selected to mimic as closely as possible natural canopy shade, and moderately high light of insufficient irradiance to induce photoinhibitory or photoprotective responses (300 μmol m−2 s−1). Light-and CO2-saturated photosynthetic rates of oxygen evolution (Pmax) and chlorophyll content were measured. Large variation was found in both parameters, and two ‘strategies’ for long-term acclimation were identified: firstly a change in chlorophyll per unit leaf area which was found to correlate positively with photosynthetic capacity, and secondly changes in chlorophyll alb ratio and Pmax, indicative of alterations at the chloroplast level, which were not associated with a change in chlorophyll content per unit leaf area. Combinations of these two strategies may occur, giving rise to the observed diversity in photosynthetic acclimation. The extent and nature of photosynthetic acclimation were compared with an index of shade association, calculated from the association each species has with woodland. It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in ‘sun’ species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level. A framework for explaining the variation between plant species in leaf-level photosynthetic capacity, in relation to the natural light environment, is presented. This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.
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- Chl alb
ratio of chlorophyll a to chlorophyll b
low irradiance far-red enriched growth, light
light harvesting complex associated with PSII
moderate irradiance, white growth light
photosynthetically active radiation
light- and CO2- saturated photosynthetic rate
Ribulose 1,5-bisphospahate carboxylase/oxygenase
specific leaf fresh weight