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Title: Transpiration-induced axial and radial tension gradients in trunks of Douglas-fir trees.
Author: Domec, J.C.; Meinzer, F. C.; Gartner, B. L.; Woodruff, D.;
Source: Tree Physiology. 26: 275-284
Publication Series: Miscellaneous Publication
Description: We determined the axial and radial xylem tension gradients in trunks of young Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Axial specific conductivity (ks-a) and sap flux density (Js) were measured at four consecutive depths within the sapwood at a stem height of 1 m. By definition, at a given position in the bole, Js is a function not only of ks-a, but also of the driving force for water movement. The Js:ks-a ratio was therefore used to estimate axial tension gradients and the radial gradients at a stem height of 1 m were calculated from the differences in axial tension gradients at each depth. Tracheid lumen diameter and tracheid length were used to predict differences in ks-a and its divergence from the theoretical ks-a determined by the Hagen Poisseuille equation. The ratio of ks-a (determined in the laboratory) to Js (measured in the field) varied with depth in the sapwood, resulting in non-uniform axial and radial tension gradients from inner to outer sapwood. Transpiration-induced axial tension gradients were in the range of 0.006-0.01 MPa m-1 excluding the gravitational tension gradient. At a stem height of 1 m, radial tension gradients were in the range of 0.15-0.25 MPa m-1 and were lower in the middle sapwood than in the inner or outer sapwood. Axial tension gradients were 44-50% higher in the outer sapwood than in the inner sapwood. At a stem height of 1 m, radial Js calculated on the basis of radial tension gradients and measured radial specific conductivity (ks-a), was about two orders of magnitude smaller than axial Js. Our findings indicate that large radial tension gradients occur in the sapwood and clarify the role played by xylem ks-a and ks-a in determining in situ partitioning of Js in the axial and radial directions.
Keywords: sap flux density, specific conductivity, xylem anatomy, xylem embolism
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Domec, J.C.; Meinzer, F. C.; Gartner, B. L.; Woodruff, D. 2006. Transpiration-induced axial and radial tension gradients in trunks of Douglas-fir trees. Tree Physiology. 26: 275-284
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