Hydraulic conductance and xylem anatomy in fruit tree shoots

Hydraulic conductance is an important index of water flow in plants. We constructed a simple device for measuring the relative hydraulic conductance of fruit tree shoots. The values of vines (kiwifruit and grape) were the highest among 17 species of major temperate fruit trees, followed by deciduous trees (e.g. chestnut, Japanese pear, and peach), evergreen citrus trees (e.g. Kawanonatsudaidai and Satsuma mandarin), and loquat. The diameter and number of vessels and total vessel area in shoots were calculated with image analysis software from photomicrographs of 13 of the species. The diameter of the vessels was largest in vines (kiwifruit and grape), followed by persimmon and chestnut, and smallest in deciduous trees (e.g. apple and Japanese apricot), citrus, and loquat. Relative hydraulic conductance had a higher correlation with the water flow index (Sigma r(4)/S x (xylem ratio)), calculated from the diameter and number of vessels in the xylem according to the Hagen-Poiseuille law, and than with total vessel area per unit of shoot cross-sectional area.