PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Does lateral CO₂ diffusion inside leaves from shaded to illuminated leaf areas affect photosynthesis efficiency? Roland Pieruschka^*,1, Siegfried Jahnke¹, Manfred Jensen², Ulrich Schurr¹, ¹ Forschungszentrum Jülich, Jülich, Germany² Universität Duisburg-Essen, Essen, Germany

ABSTRACT- Leaf anatomy affects lateral gas diffusion within intercellular air spaces of leaves. In heterobaric leaves, bundle sheath extensions span between lower and upper epidermis and prevent lateral gas transport. Homobaric leaves lack bundle sheath extensions and are characterized by large interconnected intercellular air space with few or no barriers for lateral gas fluxes (Neger 1918). It has been shown that this has consequences for gas exchange measurement (Jahnke & Krewitt 2002). However, we hypothesize that these structure-function relations will also affect gas exchange under natural conditions: distribution of light within a canopy is very heterogeneous, only leaves at the outermost canopy are fully exposed to light, whereas the leaves underneath are often partly shaded. Respiratory processes may dominate in the shaded parts while in the adjacent illuminated leaf parts photosynthetic CO₂ uptake prevails. Quantum yield efficiency as measured by chlorophyll fluorescence imaging was significantly higher at the margin of a shaded leaf area compared to more distant leaf parts. Obviously, shading caused lateral CO₂ flux to the illuminated leaf parts. This effect became more pronounced at low stomatal conductance. In particular, plants under drought stress may benefit from higher internal CO₂ concentration (c_i) in illuminated leaf parts adjacent to a shadow, which causes an increase in photosynthetic efficiency and reduces photoinhibitory effects in these areas. Internal refixation of laterally transported respiratory CO₂ within homobaric leaves may thus increase the water use efficiency of a plant.

KEY WORDS: lateral gas diffusion, drought stress, homobaric leaf anatomy, chlorophyll fluorescence