Water transport in the liana Bauhinia fassoglensis (Fabaceae)
Ewers F; Fisher J; Chiu S
To determine the efficiency of xylem conductance in the liana (woody vine) Bauhinia fassoglensis Kotschy ex Schweinf. we measured hydraulic conductance per unit stem length (measured Kh) leaf-specific conductivity (LSC = Kh/distal leaf area) transpiration rate (E) xylem water potential (Œµ) vessel number and vessel diameter. The measured Kh was 49% (se = 7%) of the predicted Kh from Poiseuille\s law. The mean LSC for unbranched stem segments was 1.10 vó 10‚àí8 square meters per megapascal per second (se = 0.07). LSCs were much lower (about 0.2) at branch junctions. At midday with E at 7 vó 10‚àí8 meters per second the measured drop in Œµ was about 0.08 megapascal per meter along the stems and branches and about 0.27 megapascal in going from stem to leaf. In addition there was a drop of about 0.20 megapascal at branch junctions as predicted by E/LSC. In diurnal measurements leaf Œµ never dropped below about ‚àí1.2 megapascal. For long (e.g. 16 meters) stems the predicted mid-day drop in Œµ through the xylem transport system might be great enough to have substantial physiological impact.