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- W2997233068 abstract "The xylem in plants is formed by interconnected dead cells that allow the flow of water from the roots to the leaves. The ascent of sap is mainly passive and it is driven by water evaporation from the mesophyll cell walls in the leaf. The water evaporation generates capillary suction on the menisci at the micro-porous of cell walls, causing negative hydrostatic pressure that propagates down the water column in the xylem. Due to plants grow in height the length of the hydraulic path increases progressively posing the question whether the hydraulic resistance increases accordingly. There is evidence that plants have evolved xylem structures that compensate the possible increase of the hydraulic resistance imposed by path length, namely the tip-to-base conduits widening. Conduits widening has been reported in several species, both angiosperms and conifers, showing that the degree of widening from tip to the base of the stem is very similar among species, or in other words, that plants converge towards a universal xylem structure. Nevertheless, several points on the hydraulic architecture of plants remain to be elucidated.A largely debated point is whether xylem anatomical traits (e.g. the absolute cell size) change with climatic conditions. Moreover, whether and how the conduits widening in the stem may affect the xylem anatomy of the leaf is still not fully understood. This PhD project aims to widen our understanding of the allometric relations of leaves and stem xylem, considering how the environmental conditions and the height of the plant affect the hydraulic architecture of the water transport system.A methodological study (Study 1) has been performed on the xylem tissue of stems of Acacia trees grown in different water availability conditions. The main result was that, once the anatomical data were standardized for the tree height, the hydraulic architecture of the xylem did not change in relation to the environmental conditions.Two studies have been performed on the hydraulic architecture of leaves. The main focus was on the anatomical traits of the xylem conduits in relation to the leaf dimensions and/or the position in the tree crown (height from the base of the stem). The main results were that the xylem traits scaled with the leaf area independently by the position in the crown (Study 2). A fine analysis of the leaf midrib (i.e. major leaf vein) has shown a rigid hydraulic architecture and tissues coordination (Study 3) that was well predicted by the distance from the leaf tip. Both studies showed that the dimensions of the terminal veins were conserved among leaves and within leaf suggesting that the hydraulic architecture of the xylem in the leaf evolved in a way to guarantee an equal distribution of the hydraulic resistances (and thus of the water) among leaves and within the leaf lamina.Finally, we implemented the anatomical data of both stem and leaf into a hydraulic model to assess the distribution of resistances along the hydraulic path to evaluate how the anatomy of the transport system affects the physiology of the entire tree (Study 4).This thesis has highlighted that the path length (i.e. the height of the plant and the dimensions of the leaf) is the main factor affecting the hydraulic architecture of the tree. The conduit dimension in both stem and leaf are determined by the distance from the terminal parts, stem apex or leaf tip respectively. Climatic conditions resulted to have marginal (non-significant) effect on the stem anatomical traits. In the leaf, the dimensions of the xylem conduits are statistically invariant with changes in plant size. This rigid hydraulic architecture of the tree, from the stem to the leaf, allows minimizing the effect of the path length on the hydraulic resistance, confining nearly the whole gradient of water potential within the leaves." @default.
- W2997233068 created "2020-01-10" @default.
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- W2997233068 date "2019-02-25" @default.
- W2997233068 modified "2023-09-27" @default.
- W2997233068 title "The hydraulic architecture of the plants: study of the allometric relations in stem and leaves" @default.
- W2997233068 hasPublicationYear "2019" @default.
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