Shade-tolerant species are considered to show faster photosynthetic induction responses to sunflecks than intolerants. However, conflicting results emerged from previous work are probably due to inconsistency in growth light environment. Quantification of the influences of shade tolerant and growth light environment on induction responses is lacking.
Thus, this study aimed to answer following questions: (1) Do shade-tolerant species really show faster induction responses to simulated sunflecks than shade-intolerants? (2) If so, or any interspecific differences in induction responses are found, what is the (main) cause? (3) How do photosynthetic induction responses in seedlings within each species respond to individual light environment?
Photosynthetic dynamics following an increase in irradiance were investigated in six species in this study, three shade-tolerant and three -intolerant. At least five seedlings from contrasting light microhabitats were chosen for each species. We also followed chlorophyll fluorescence dynamics during induction and measured stomatal morphology characteristics.
Results/Conclusions
Significant differences between shade-tolerant species and –intolerant species were only found in steady-state parameters instead of photosynthetic induction responses. Photosynthetic induction responses were acclimated to growth light environment. As potential sunfleck ratio increased, induction time increased due to slower activation of Rubisco activation. Shade-tolerant species showed larger variations in induction responses than intolerant species. Limitation from electron transport was not completely relaxed until 10 min after light increased. No relationship existed between stomatal morphology characteristics and stomatal behavior.
Our results suggest that species with contrasting shade tolerance differ in their induction responses plasticity induced by light regimes, rather than induction responses per se. Slower induction responses under brighter microhabitats may be a side effect of the increase in steady-state assimilation rate.