The effect of growth irradiance on leaf anatomy and photosynthesis in Acer species differing in light demand
Variation in light demand is a major factor in determining the growth and survival of trees in a forest. There is strong relation between the light-demand and the effect of growth irradiance on leaf morphology and photosynthesis in three Acer species: A. rufinerve (light-demanding), A. mono (intermediate) and A. palmatum (shade-tolerant). The increase in mesophyll thickness and surface area of chloroplasts facing the intercellular airspaces (Sc) with growth irradiance was highest in A. rufinerve. Although the increase in light-saturated photosynthesis (Amax) was similar among the species, the increase in water use efficiency (WUE) was much higher in A. rufinerve than that in the other species, indicating that the response to water limitation plays an important role in leaf photosynthetic acclimation to high light in A. rufinerve. The low CO2 partial pressure at the carboxylation site (Cc) in A. rufinerve (130 µmol mol−1) at high irradiance was caused by low stomatal and internal conductance to CO2 diffusion, which minimized the increase in Amax in A. rufinerve despite its high Rubisco content. Under shade conditions, interspecific differences in leaf features were relatively small. Thus, difference in light demand related to leaf acclimation to high light rather than that to low light in the Acer species.