The xylem sap of maple (<i>Acer platanoides</i>) trees—sap obtained by a novel method shows changes with season and height

Abstract

Xylem sap of log pieces of maple trees was collected by a novel pressure/decompression method developed recently for the mechanical drying of timber. Seasonal changes and spatial distributions of the osmotic potential, the pH and the concentrations of major solutes and of the plant stress-hormone abscisic acid (ABA) were investigated. Sucrose and quebrachitol were the main components of the xylem sap. The sucrose concentration varied between 10 mM and 25 mM during the winter months and declined to a minimum during the period of bud burst. Quebrachitol was found in concentrations of up to 7 mM with a high variability throughout the year. High concentrations of ABA were measured during the summer season and in mid-winter. Rainfall caused an increase of ABA in some samples. The osmotic potential of the xylem sap increased with the height of the collection site. The pH of the sap decreased by approximately one unit between the base of the trunk and the crown. The increase of the osmotic potential was mainly due to sucrose, quebrachitol and potassium. Malate contributed to the decrease of the pH. ABA of the xylem sap increased with decreasing moisture content of the wood.