Xylem conductivities in leaf veins

Abstract Leaves are the main photosynthetic organs of plants. There is almost an infinite variety of leaf shapes and venations. The purpose of the current study was to determine if leaf areas, leaf veins and xylem conductivities are well scaled among primary, secondary and tertiary tiers in leaves with percurrent leaf venation for 32 species. Data from both fully-expanded leaves and leaves that underwent expansion were analyzed. Thirty-two species with leaves of 7.25 to 887 cm2 lamina areas with a median leaf area of 81 cm2 were tested. On average, leaves had 19 secondary veins 45 mm long to produce secondary areas of 4.1 cm2. Leaves had 272 tertiary areas, each 0.30 cm2, in which the median tertiary veins were 10 mm in length. There were strong relationships between lamina areas, vein lengths, vessel numbers, vessel radii and xylem conductivities among tier levels. Primary veins had a median xylem conductivity of 1.02 g cm-1 MPa-1 s-1 while secondary and tertiary xylem conductivities were 0.51 and 0.00081 g cm-1 MPa-1 s-1, respectively. The above strong relationships for fully-expanded leaves were confirmed for five species during leaf expansion. Estimates of water conduction with respect to lamina areas, vein characteristics and xylem conductivities among tier levels are presented. The strong relationships among the above parameters of this study suggest that leaf characteristics of leaf lamina areas, veins lengths and xylem conductivities of each species are well scaled to provide water to all areas of leaves.