Contribution of intercellular reflectance to photosynthesis in shade leaves

Abstract

The potential contribution of intercellular light reflectance to photosynthesis was investigated hy innitrating shade leaves with mineral oil. Inllltration of leaves of Hydrophyllum canadense and Asarum canadense with mineral oil decreased adaxial leaf reflectance but increased transmittance. As a result of the large increase in transmittance, infiltration caused a deerease in absorptance of 25% and 30% at 55t) and 750 nm, respectively. Thus, intercellular rellectance increa.sed absorptance in these species by this amount. In a comparison of sun and shade leaves oi Acer saccharum and Parthenocissus qtiinquefolia, oil infiltration decreased absorptance more in shade than in sun leaves. This difference suggests that the higher proportion of spongy mesophyll in shade leaves may increase internal light scattering and thus absorptance. The importance of the spongy mesophyll in increasing internal reflectance was also evident in comparisons of the optics of Populus leaves and in the fluorescence yield of oilinfiltrated leaves of several sun and shade species. Oil infiltration decrea.sed the quantum yield of fluoreseence (Fo) by 39-52% for shade leaves but only 21-25% for sun leaves. We conclude that the greater proportion of spongy parenchyma in shade leaves increased intercellular light scattering and thus absorptance. Direct measurenients with fibre-optic light probes of the distribution of light inside leaves of Hydrophyllum canadense confirmed that oil infiltration decreased the amount of back-scattered light and that most of the light scattering for this species occurred from the middle of the palisade layer to the middle of the spongy me.sophyll. We were not, however, able to assess the potential contribution of reflectance from the internal abaxial epidermis to total internal light scattering in these experiments. Using a mathematical model to compare the response of net photosynthesis (O2 flux) to incident irradiance for control leaves of H. canadense and theoretical leaves with no intercellular reflectance, we calculated that intercellular reflectance caused a 1-97-fold increase in photosynthesis at 20^molm"^s"' (incident photon flux density). This enhancement of ab.sorption and photosynthesis by inter-

Leaf optical properties of two liana species Canavalia parviflora Benth. and Gouania virgata Reissk in different light conditions

“…As pointed out by these authors, the increase in absorptance may be partially explained by an increase in chlorophyll content under shade and not by a thinning of the leaf. This was probably the case for C. parviflora, since this species showed higher chlorophyll content and was less responsive to specific leaf area than G. virgata (their leaves were thicker than DeLucia et al 1996). Thus, it is possible that absorption was enhanced under 1.5% PFD in C. parviflora by low-light alterations in leaf anatomy maximizing the effective pathlenght of a radiation beam (Lee & Graham 1986, Vogelmann 1993.…”

Seasonal leaf dimorphism in Potentilla argentea L. var. tenuiloba (Jord.) Sw. (Rosaceae)

“…P. argentea autumn leaves were thinner and had more LA with respect to the summer leaves. The larger and thinner leaves in autumn are more advantageous for light capture under low light (CARPENTHER and SMITH 1981, DE LUCIA et al 1996, POORTER 1999, WILSON et al 1999. Moreover, small-sized, thick, summer leaves provide less surface area for the loss of water through transpiration (e.g., RHIZOPOULOU and MITRA- KOS, 1990, BAKER-BROSH and PEET 1997, FALSTER and WESTOBY 2003, HUFF et al 2003.…”

Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profiles

“…The shapes of the 14 C-fixation profiles are also similar to the fluorescence profiles when leaves were irradiated on their adaxial versus abaxial surface (Sun 1996), adding further support to the view that chlorophyll fluorescence profiles may be used to predict profiles of photosynthesis within leaves. In terms of evaluating the functional significance of leaf anatomy with respect to photosynthesis, it is clear that the optical properties of the leaf mesophyll strongly influence the potential shapes of the internal photosynthesis profiles (Terashima & Hikosaka 1995;DeLucia et al 1996;Smith et al 1997;Richter & Fukshansky 1998;Evans 1999). The widespread occurrence of palisade mesophyll in leaves which facilitates the penetration of light (Vogelmann & Martin 1993), and the anatomical variation between sun and shade leaves suggest that leaves adjust their anatomy to control how light migrates through the mesophyll (Vogelmann 1993;Vogelmann, Nishio & Smith 1996).…”