| Abstract: | The effect of stem segment length on conductance measurementswas determined by repeatedly shortening the transport distancein isolated stem segments of Lonicera fragrantissima. If vesselends limit water flow, shorter segment lengths could resultin higher readings of Kh (hydraulic conductance per unit pressuregradient). The mean Kh in the successively shortened segmentsshowed no statistically significant change when shortened from20 to 2 cm, even though maximum vessel lengths ranged from 6to 14 cm. This suggests vessel ends may be less limiting towater flow than are vessel lumens. There was a statisticallysignificant drop in Kh (19%, s.e.=0·29%) when segmentswere shortened from 2 to 1 cm, regardless of the position ofthe segment within the branch. The Kh remained constant withapplied pressure in 2 cm segments while it was more variablewith applied pressure in 1 cm segments. Based on the paint-infusionmethod mean vessel lengths were from 0·6 to 1·2cm. The consistently lower Kh in 1 cm segments might be dueto an end effect in segments with a high percentage of cut openvessels. Within a branch, distal and proximal stem segmentshad lower Kh values than segments from intermediate positions,but nodes had no measurable impact on Kh. Longer segments allowfor more accurate and consistent measurements of Kh since theyintegrate localized variation in Kh while minimizing the segmentend effect. Key words: Vessel length, vessel end, hydraulic conductance, paint-infusion method, Lonicera fragrantissima |
