Gas diffusion through wood: implications for oxygen supply |
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Authors: | Johannes Sorz Peter Hietz |
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Institution: | (1) Department of Integrative Biology, Institute of Botany, University of Natural Resources and Applied Life Sciences (BOKU), Gregor Mendel-Str. 33, 1180 Vienna, Austria |
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Abstract: | Living tissue in tree stems has to be supplied with oxygen, which can be transported upwards with the transpiration stream;
but in times of zero sapflow, the only source is the oxygen stored or diffusing radially through bark and xylem. We measured
radial and axial diffusion of oxygen against nitrogen gas in wood of coniferous (Picea abies (L.) Karst. and Taxus baccata L.), ring-porous (Quercus robur L. and Fraxinus excelsior L.) and diffuse-porous (Fagus sylvatica L. and Carpinus betulus L.) trees at different water and gas contents in the laboratory. The diffusion coefficient (D) in radial direction was mostly between 10−11 and 10−7 m2 s−1 and was strongly related to the gas content. At 40% gas volume, D increased 5–13-fold in Picea, Taxus and Quercus, 36-fold in Fraxinus, and about 1000-fold in Carpinus and Fagus relative to D at 15% gas volume. In the axial direction, diffusion was 1 or 2 orders of magnitude faster. Between-species differences in
diffusion velocities can largely be explained by wood structure. In general, D was lowest in conifers, highest in diffuse-porous and intermediate in ring-porous hardwoods, where the large vessels were
mostly blocked by tyloses. Model calculations showed that at very high water content, radial diffusion can be too low to ensure
the supply of respiring sapwood with sufficient oxygen and an important function of gas in living stems appears to be the
supply of oxygen through storage and diffusion. |
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Keywords: | Gas diffusion Oxygen supply Wood structure |
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