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The radial and azimuthal (or tangential) distribution of sap velocity in tree Stems - Why and can we predict it?
Year:
2012
Source of publication :
Acta Horticulturae
Authors :
Cohen, Shabtai
;
.
Volume :
951
Co-Authors:
Cohen, S., Dept. of Env. Physics and Irrigation, Inst. Soil, Water and Env. Sciences, ARO Volcani Center, Bet Dagan, Israel
Wheeler, J., Dept. of Organismic and Evol. Biol., Harvard U. Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, United States
Holbrook, N.M., Dept. of Organismic and Evol. Biol., Harvard U. Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, United States
Facilitators :
From page:
131
To page:
138
(
Total pages:
8
)
Abstract:
Sap flux density is highly variable in arboreal woody angiosperm and gymnosperm stems in the radial, azimuthal (or tangential) and axial directions, presenting a challenge to the determination of total flux from measurements made with point sensors. This paper focuses on the variability, its quantification and explanation. Sap flows through conduits with diameters in the order of 10'sto about 500 microns. There are usually many thousands of operational conduits in a woody stem. Sap flux point sensors are typically in contact with a few mm2 to tens of mm2 of xylem and measure flux in nearby undisturbed xylem. Thus if the distribution of active conduits were random, we would expect only a small amount of variability in sap flux measurements. In the radial direction, sap flux is concentrated in the outer part of the xylem. This roughly corresponds with the sapwood, sometimes defined as the part of the xylem containing living parenchyma cells. But the extent of sap flux does not strictly conform to the sapwood, and in the radial direction can vary widely. In the majority of cases studied, sap flux density decreases with depth in the stem, and is significant to a depth of about 5 cm. Some presentations of sap flux density variations with depth relate the decline in flux density with the percent of stem radius traversed, but empirical evidence suggests that after the stem exceeds a radius of several cms, taking a fixed depth may be more representative of the hydraulically active depth for the majority of species. Similarly, changes in sapwood width as trees age are minor. Variability in the tangential direction in the xylem can be large and less predictable. Its quantification is important for determining how many probes should be inserted in order to reduce the standard error of the mean to pre-defined limits. Initial results suggest that the coefficient of variation in the tangential direction is larger in hardwoods than in softwoods. Variability in the axial direction has rarely been studied per se. Most interest in this case has been in studying time lags in sap flux and capacitance of stems. Xylem conduit diameters at the base of the stem increase as tree height increases. This would suggest that sap velocity in individual elements would increase with height in the stem.
Note:
Related Files :
anatomy
Gymnospermae
Magnoliophyta
sap flow
xylem
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Related Content
More details
DOI :
Article number:
Affiliations:
Database:
Scopus
Publication Type:
Conference paper
;
.
Language:
English
Editors' remarks:
ID:
30687
Last updated date:
02/03/2022 17:27
Creation date:
17/04/2018 00:56
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Scientific Publication
The radial and azimuthal (or tangential) distribution of sap velocity in tree Stems - Why and can we predict it?
951
Cohen, S., Dept. of Env. Physics and Irrigation, Inst. Soil, Water and Env. Sciences, ARO Volcani Center, Bet Dagan, Israel
Wheeler, J., Dept. of Organismic and Evol. Biol., Harvard U. Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, United States
Holbrook, N.M., Dept. of Organismic and Evol. Biol., Harvard U. Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, United States
The radial and azimuthal (or tangential) distribution of sap velocity in tree Stems - Why and can we predict it?
Sap flux density is highly variable in arboreal woody angiosperm and gymnosperm stems in the radial, azimuthal (or tangential) and axial directions, presenting a challenge to the determination of total flux from measurements made with point sensors. This paper focuses on the variability, its quantification and explanation. Sap flows through conduits with diameters in the order of 10'sto about 500 microns. There are usually many thousands of operational conduits in a woody stem. Sap flux point sensors are typically in contact with a few mm2 to tens of mm2 of xylem and measure flux in nearby undisturbed xylem. Thus if the distribution of active conduits were random, we would expect only a small amount of variability in sap flux measurements. In the radial direction, sap flux is concentrated in the outer part of the xylem. This roughly corresponds with the sapwood, sometimes defined as the part of the xylem containing living parenchyma cells. But the extent of sap flux does not strictly conform to the sapwood, and in the radial direction can vary widely. In the majority of cases studied, sap flux density decreases with depth in the stem, and is significant to a depth of about 5 cm. Some presentations of sap flux density variations with depth relate the decline in flux density with the percent of stem radius traversed, but empirical evidence suggests that after the stem exceeds a radius of several cms, taking a fixed depth may be more representative of the hydraulically active depth for the majority of species. Similarly, changes in sapwood width as trees age are minor. Variability in the tangential direction in the xylem can be large and less predictable. Its quantification is important for determining how many probes should be inserted in order to reduce the standard error of the mean to pre-defined limits. Initial results suggest that the coefficient of variation in the tangential direction is larger in hardwoods than in softwoods. Variability in the axial direction has rarely been studied per se. Most interest in this case has been in studying time lags in sap flux and capacitance of stems. Xylem conduit diameters at the base of the stem increase as tree height increases. This would suggest that sap velocity in individual elements would increase with height in the stem.
Scientific Publication
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