THE XYLEM SAP OF MAPLE (ACER-PLATANOIDES) TREES - SAP OBTAINED BY A NOVEL METHOD SHOWS CHANGES WITH SEASON AND HEIGHT

Xylem sap of log pieces of maple trees was collected by a novel pressu re/decompression method developed recently for the mechanical drying o f timber. Seasonal changes and spatial distributions of the osmotic po tential, the pH and the concentrations of major solutes and of the pla nt stress-hormone abscisic acid (ABA) were investigated. Sucrose and q uebrachitol were the main components of the xylem sap. The sucrose con centration varied between 10 mM and 25 mM during the winter months and declined to a minimum during the period of bud burst, Quebrachitol wa s found in concentrations of up to 7 mM with a high variability throug hout the year, High concentrations of ABA were measured during the sum mer season and in mid-winter, Rainfall caused an increase of ABA in so me samples. The osmotic potential of the xylem sap increased with the height of the collection site. The pH of the sap decreased by approxim ately one unit between the base of the trunk and the crown, The increa se of the osmotic potential was mainly due to sucrose, quebrachitol an d potassium, Malate contributed to the decrease of the pH. ABA of the xylem sap increased with decreasing moisture content of the wood.