%0 Journal Article %1 Sacketal_04 %A Sack, L. %A Streeter, C. M. %A Holbrook, N. M. %D 2004 %J Plant Physiology %K anatomy, bibtex-import, citeulikeExport grass, hydraulics, kleaf, leaf, techniques %P 1824--1833 %T Hydraulic analysis of water flow through leaves of sugar maple and red oak %V 134 %X Leaves constitute a substantial fraction of the total resistance to water ?ow through plants. A key question is how hydraulic resistance within the leaf is distributed among petiole, major veins, minor veins, and the pathways downstream of the veins. We partitioned the leaf hydraulic resistance (Rleaf) for sugar maple (Acer saccharum) and red oak (Quercus rubra) by measuring the resistance to water ?ow through leaves before and after cutting speci?c vein orders. Simulations using an electronic circuit analog with resistors arranged in a hierarchical reticulate network justi?ed the partitioning of total Rleaf into component additive resistances. On average 64\% and 74\% of the Rleaf was situated within the leaf xylem for sugar maple and red oak, respectively. Substantial resistance?32\% and 49\%? was in the minor venation, 18\% and 21\% in the major venation, and 14\% and 4\% in the petiole. The large number of parallel paths (i.e. a large transfer surface) for water leaving the minor veins through the bundle sheath and out of the leaf resulted in the pathways outside the venation comprising only 36\% and 26\% of Rleaf. Changing leaf temperature during measurement of Rleaf for intact leaves resulted in a temperature response beyond that expected from changes in viscosity. The extra response was not found for leaves with veins cut, indicating that **water crosses cell membranes after it leaves the xylem. The large proportion of resistance in the venation can explain why stomata respond to leaf xylem damage and cavitation. The hydraulic importance of the leaf vein system suggests that the diversity of vein system architectures observed in angiosperms may re?ect variation in whole-leaf hydraulic capacity.

@article{Sacketal_04, abstract = {{Leaves constitute a substantial fraction of the total resistance to water ?ow through plants. A key question is how hydraulic resistance within the leaf is distributed among petiole, major veins, minor veins, and the pathways downstream of the veins. We partitioned the leaf hydraulic resistance (Rleaf) for sugar maple (Acer saccharum) and red oak (Quercus rubra) by measuring the resistance to water ?ow through leaves before and after cutting speci?c vein orders. Simulations using an electronic circuit analog with resistors arranged in a hierarchical reticulate network justi?ed the partitioning of total Rleaf into component additive resistances. On average 64\% and 74\% of the Rleaf was situated within the leaf xylem for sugar maple and red oak, respectively. Substantial resistance?32\% and 49\%? was in the minor venation, 18\% and 21\% in the major venation, and 14\% and 4\% in the petiole. The large number of parallel paths (i.e. a large transfer surface) for water leaving the minor veins through the bundle sheath and out of the leaf resulted in the pathways outside the venation comprising only 36\% and 26\% of Rleaf. Changing leaf temperature during measurement of Rleaf for intact leaves resulted in a temperature response beyond that expected from changes in viscosity. The extra response was not found for leaves with veins cut, indicating that **water crosses cell membranes after it leaves the xylem. The large proportion of resistance in the venation can explain why stomata respond to leaf xylem damage and cavitation. The hydraulic importance of the leaf vein system suggests that the diversity of vein system architectures observed in angiosperms may re?ect variation in whole-leaf hydraulic capacity.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Sack, L. and Streeter, C. M. and Holbrook, N. M.}, biburl = {https://www.bibsonomy.org/bibtex/2dcde489a840b9f0a10cfa6af3fcdd6d6/dianella}, citeulike-article-id = {1523577}, comment = {(private-note)the temperature dependency was accountable for by changes in viscosity in the cut leaves, but was much too great for that in intact leaves Kleaf - Kpetiole = Klamina Even with cutting, 60\%+ of Klamina remained, so that's why they concluded that a fair amount of resistance was in the large veins. The topology of the minor vein network places the segments essentially in parallel. Because resistors in parallel are inversely additive, shorting even a small number has a large effect on the total network resistance. One aspect of the hydraulic architecture of leaf venation that contributes to the minor veins acting as in parallel, irrespective of their position, is a relatively large resistance at the major- minor vein junctions. orders. Two studies have examined Rleaf in monocots by measuring longitudinal resistance in leaf segments (effectively driven by the dimensions and numbers of the largest longitudinal conduits) to parameterize a model of the hydraulic architecture as a single longitudinal vein, with lateral radial leaks (Wei et al., 1999; Martre et al., 2001). These studies concluded that most of the resistance to ?ow was outside the vena- tion. Although it is possible that in grasses Routside veins is a larger component of Rleaf than in dicotyledonous leaves with more vein orders, modeling the vein system of grasses as a collection of parallel pipes may, to some degree, neglect the actual distribution network. In grass leaves the major longitudinal veins constitute as little as 30\% of the total vein density (Canny, 1990). Large veins may dominate axial trans- port, but smaller longitudinal and transverse veins with conduit diameters and numbers only 20\% to 50\% of those in the large longitudinal veins may in fact distribute most water to the mesophyll (Colbert and Evert, 1982; Altus and Canny, 1985; Altus et al., 1985; Canny, 1990). Across plant species, Rleaf is negatively coordinated with peak rates of gas exchange (Aasamaa et al., 2001; Sack et al., 2003b).}, interhash = {933094e039abb6a4223d1ea61b1fa289}, intrahash = {dcde489a840b9f0a10cfa6af3fcdd6d6}, journal = {Plant Physiology}, keywords = {anatomy, bibtex-import, citeulikeExport grass, hydraulics, kleaf, leaf, techniques}, pages = {1824--1833}, posted-at = {2007-07-31 05:53:44}, priority = {0}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Hydraulic analysis of water flow through leaves of sugar maple and red oak}}, volume = 134, year = 2004 }