DIVERSITY OF HYDRAULIC CONDUCTANCE IN LEAVES OF TEMPERATE AND TROPICAL SPECIES: POSSIBLE CAUSES AND CONSEQUENCES

Abstract

Liquid-flow-pathway hydraulic conductances (K_L) were measured in leaves of 24 species of temperate and tropical plants. The leaves had specific leaf areas (SLA) ranging from 0.05 to 0.5 m² g^-1. Leaves with low SLA were typically sclerophylls and leaves with high SLA were typically malacophylls. No correlation was found between K_L and SLA. Whole shoot conductances were measured by transient (K₁) and quasi-steady state (K₁) methods. In the transient method, pressure (P) was increased at a rate of 3 to 5 kPas^-1, whereas in quasi-steady state measurements, P was held constant for about 15 min. Flow (F) through leaves during transient measurements was a linear function of P and passed through the origin (F = 0 at P = 0) indicating that K₁ was a first order rate constant ( F = K₁P). At low conductances, K₁ was up to 9.3% more than K₁ . This difference is tentatively ascribed to polarisation of solutes across membranes during quasi-steady state measurements. Implications of low leaf conductances on the measurement of xylem pressure potential with a Scholander-Hammel pressure bomb are also discussed.