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dc.contributor.authorRamirez Carvalho, Monica
dc.identifier.otherbibid: 10361621
dc.description.abstractThe phloem and the xylem form the plant hydraulic system that mediates long-distance water, nutrient, and signaling transport necessary for survival and growth. In leaves, these microfluidic tissues are formed as files of tracheary and sieve elements that ensure the effective distribution of water and the collection of sugars throughout the lamina. The xylem provides the water required to compensate for water losses during CO2 uptake, and the phloem collects sugar and provides the osmotically-mediated pressure differential between sources and sinks required for long-distance transport. Whereas form-function relations of xylem hydraulics have been extensively studied in numerous species and organs, comparatively little is known about many of the basic structural properties of phloem that have direct effects on sap translocation. Using a combination of light, fluorescent, multiphoton, and transmission electron microscopy, I quantify and compare the phloem and xylem hydraulic structure in two topologically distinct leaf types, Ginkgo and Populus x canescens, which have leaves with an open dichotomous venation pattern and a hierarchical reticulate pattern, respectively. In both leaf types, phloem and xylem hydraulic transport areas scale isometrically across all leaf vein levels. The conductive areas of individual veins, as well as the cross-sectional areas and lengths of sieve and tracheary elements increase from minor veins to the petiole in poplar, and from the leaf margin to the leaf base in Ginkgo. This pattern effectively increases sap flow as sugars exit the leaf. At the whole leaf level, however, the hydraulic structure of both leaf types differs significantly. The scaling of Ginkgo hydraulics complies with that observed in single-veined leaves of other gymnosperms, and is consistent with theoretical models based on phloem transport that minimize flow energy dissipation. The leaf hydraulic structure of both leaf types is consistent with the predictions of Münch’s Pressure Flow Hypothesis. Finally, previously used models for describing vascular branching render themselves too simplistic and fail to describe the hydraulic geometry of Ginkgo or poplar leaves. However, the scaling of conductive diameters across vein branching levels are consistent with da Vinci’s area-preservation model, and not with Murray’s law of volumetric conservation.
dc.subjectPlant sciences
dc.titleLeaf Hydraulic Geometry
dc.typedissertation or thesis Biology University of Philosophy D., Plant Biology
dc.contributor.chairNiklas, Karl Joseph
dc.contributor.committeeMemberOwens, Thomas G.
dc.contributor.committeeMemberTurgeon, E G Robert

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