The sapwood/heartwood transition is hydraulically determined by the combined effects of conduit widening, tree height, and height growth rate on the contribution of inner rings to the total xylem conductance.The size-related xylem adjustments required to maintain a constant leaf-specific sapwood conductance (K-LEAF) with increasing height (H) are still under discussion. Alternative hypotheses are that: (i) the conduit hydraulic diameter (Dh) at any position in the stem and/or (ii) the number of sapwood rings at stem base (NSWr) increase with H. In addition, (iii) reduced stem elongation (& UDelta;H) increases the tip-to-base conductance through inner xylem rings, thus possibly the NSWr contributing to K-LEAF. A detailed stem analysis showed that Dh increased with the distance from the ring apex (DCA) in all rings of a Picea abies and a Fagus sylvatica tree. Net of DCA effect, Dh did not increase with H. Using sapwood traits from a global dataset, NSWr increased with H, decreased with & UDelta;H, and the mean sapwood ring width (SWrw) increased with & UDelta;H. A numerical model based on anatomical patterns predicted the effects of H and & UDelta;H on the conductance of inner xylem rings. Our results suggest that the sapwood/heartwood transition depends on both H and & UDelta;H, and is set when the carbon allocation to maintenance respiration of living cells in inner sapwood rings produces a lower gain in total conductance than investing the same carbon in new vascular conduits.

Axial conduit widening, tree height, and height growth rate set the hydraulic transition of sapwood into heartwood

Petit, Giai
;
Carrer, Marco;Prendin, Angela Luisa;
2023

Abstract

The sapwood/heartwood transition is hydraulically determined by the combined effects of conduit widening, tree height, and height growth rate on the contribution of inner rings to the total xylem conductance.The size-related xylem adjustments required to maintain a constant leaf-specific sapwood conductance (K-LEAF) with increasing height (H) are still under discussion. Alternative hypotheses are that: (i) the conduit hydraulic diameter (Dh) at any position in the stem and/or (ii) the number of sapwood rings at stem base (NSWr) increase with H. In addition, (iii) reduced stem elongation (& UDelta;H) increases the tip-to-base conductance through inner xylem rings, thus possibly the NSWr contributing to K-LEAF. A detailed stem analysis showed that Dh increased with the distance from the ring apex (DCA) in all rings of a Picea abies and a Fagus sylvatica tree. Net of DCA effect, Dh did not increase with H. Using sapwood traits from a global dataset, NSWr increased with H, decreased with & UDelta;H, and the mean sapwood ring width (SWrw) increased with & UDelta;H. A numerical model based on anatomical patterns predicted the effects of H and & UDelta;H on the conductance of inner xylem rings. Our results suggest that the sapwood/heartwood transition depends on both H and & UDelta;H, and is set when the carbon allocation to maintenance respiration of living cells in inner sapwood rings produces a lower gain in total conductance than investing the same carbon in new vascular conduits.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3495252
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