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000045486 1001_ $$0P:(DE-Juel1)129379$$aPieruschka, Roland$$b0$$eCorresponding author$$gmale$$uFZJ
000045486 245__ $$aEffect of internal leaf structures on gas exchange of leaves
000045486 260__ $$aJülich$$bForschungszentrum Jülich GmbH Zentralbibliothek, Verlag$$c2005
000045486 300__ $$a120 S.
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000045486 4900_ $$0PERI:(DE-600)2414988-3$$821286$$aSchriften des Forschungszentrums Jülich. Reihe Umwelt / Environment$$v56
000045486 502__ $$aUniversität Düsseldorf, Diss., 2005$$bDr. (Univ.)$$cUniversität Düsseldorf$$d2005
000045486 500__ $$aRecord converted from VDB: 12.11.2012
000045486 520__ $$aGas exchange of leaves is generally considered as the interchange of gaseous compounds between the leaf interior and ambient air. Once inside the leaf, CO$_{2}$ can diffuse along its concentration gradients mainly regarded in the vertical direction of the blade towards the assimilating tissues. Lateral gas diffusion within intercellular air spaces may be much more effective than has been considered so far which depends on anatomical features of leaves. In heterobaric leaves, lateral diffusion is restricted by bundle-sheath extensions and the mesophyll is composed of closed compartments. Homobaric leaves, however, lack such extensions and the leaves have large interconnected intercellular air spaces. The specific internal gas diffusion properties of the leaves were characterized by gas conductivities. Gas conductivity was larger in lateral than in the vertical direction of homobaric leaf blades. However, there was a large variability of the size and property of the intercellular air space among different species. When `clamp-on´ leaf chambers were used it was found that lateral diffusion inside leaves seriously affected gas exchange measurements. The impact of lateral CO$_{2}$ diffusion on gas exchange measurement was substantial when exchange rates were low. Homobaric leaves showed internal lateral gas fluxes when an overpressure was applied to the leaf chamber which has been used in commercial gas exchange systems to minimise the effects of leaks in the leaf chamber. It was found here that overpressure affected CO$_{2}$ and H$_{2}$O exchange rates of homobaric leaves substantially larger than the theoretical direct impact of air pressure on gas exchange processes. Gas gradients inside leaves emerged when a leaf part was shaded and the adjacent area of the leaf blade illuminated. Respiratory CO$_{2}$ evolved in the shaded region diffused to the illuminated area were it was fixed by photosynthesis. These processes obviously increased the photosynthetic efficiency along the light/shade borderline as was visualized by chlorophyll fluorescence imaging techniques. The recycling of respiratory CO$_{2}$ from distant shaded areas was found to be larger when stomatal conductance was low as is the case under drought stress. Thus, when a homobaric leaf was illuminated by lightflecks, additional CO$_{2}$ increased the carbon gain, water use efficiency, and reduced light stress. It was hypothesized that homobaric leaf anatomy is a trait which has evolved under certain environmental conditions.
000045486 536__ $$0G:(DE-Juel1)FUEK257$$2G:(DE-HGF)$$aChemie und Dynamik der Geo-Biosphäre$$cU01$$x0
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000045486 9131_ $$0G:(DE-Juel1)FUEK257$$bEnvironment (Umwelt)$$kU01$$lChemie und Dynamik der Geo-Biosphäre$$vChemie und Dynamik der Geo-Biosphäre$$x0
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000045486 9201_ $$0I:(DE-Juel1)VDB49$$d31.12.2006$$gICG$$kICG-III$$lPhytosphäre$$x0
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