Journal Article

The Effect of Segment Length on Conductance Measurements in Lonicera fragrantissima

SHAU-TING CHIU and FRANK W. EWERS
Journal of Experimental Botany
Vol. 44, No. 258 (January 1993), pp. 175-181
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23694351
Page Count: 7
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The Effect of Segment Length on Conductance Measurements in Lonicera fragrantissima
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Abstract

The effect of stem segment length on conductance measurements was determined by repeatedly shortening the transport distance in isolated stem segments of Lonicera fragrantissima. If vessel ends limit water flow, shorter segment lengths could result in higher readings of Kh (hydraulic conductance per unit pressure gradient). The mean Kh in the successively shortened segments showed no statistically significant change when shortened from 20 to 2 cm, even though maximum vessel lengths ranged from 6 to 14 cm. This suggests vessel ends may be less limiting to water flow than are vessel lumens. There was a statistically significant drop in Kh (19%, s.e. = 0.29%) when segments were shortened from 2 to 1 cm, regardless of the position of the segment within the branch. The Kh remained constant with applied pressure in 2 cm segments while it was more variable with applied pressure in 1 cm segments. Based on the paint-infusion method mean vessel lengths were from 0.6 to 1.2 cm. The consistently lower Kh in 1 cm segments might be due to an end effect in segments with a high percentage of cut open vessels. Within a branch, distal and proximal stem segments had lower Kh values than segments from intermediate positions, but nodes had no measurable impact on Kh. Longer segments allow for more accurate and consistent measurements of Kh since they integrate localized variation in Kh while minimizing the segment end effect.

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