The Influence of the Lignotuber on Hydraulic Conductance and Leaf Conductance in Eucalyptus behriana Seedlings

Abstract

Hydraulic conductances of stem segments and stem-plus-lignotuber segments were estimated for 3-year-old seedlings of the mallee eucalypt Eucalyptus behriana F. Muell. Stems of seedlings were cut underwater and either above or below the lignotuber. Cutting the stem of intact seedlings underwater and above the lignotuber resulted in rapid increases in leaf water potential (Ψ); 1.1 MPa in 10-15 min with a concomitant decrease in leaf conductance. Cutting the stem below the lignotuber did not significantly affect leaf Ψ or leaf conductance. Transpirational flow through whole seedlings and segments of seedlings was about 10-9 m3 s-1. The hydraulic conductance of the lignotuber (2.27 × 10-9 m3 s-1 Mpa-1) was about half that of the stem. This work suggests that resistance to water flow through the lignotuber accounts, in part, for the persistently low dawn Ψ of the foliage of mature trees of E. behriana.