Xylem sap composition of beech (Fagus sylvatica L.) trees: seasonal changes in the axial distribution of XXXX compounds.

@entity462 @entity2041 @entity1432 @entity599 @entity597
During different phases of the annual growth cycle, xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by the water displacement technique. Irrespective of the height of the trunk, both @entity597 and reduced @entity599 compounds were detected in the xylem sap throughout the year. @entity597 was the predominant @entity599 compound in all samples analyzed. Its concentration in the xylem sap varied between 10 and 350 micro mol l(-1), with highest concentrations in April, shortly before bud break. In contrast to other tree species, @entity462 and not @entity2041 was the predominant @entity1432 transported in the xylem sap of beech trees. The @entity462 concentration ranged between 0.1 and 1 micro mol l(-1). As observed for @entity597 , maximum @entity462 concentrations were found in April. Apparently, both @entity597 and @entity462 transport contribute to the @entity599 supply of the developing leaves. Seasonal changes in the axial distribution of @entity462 and @entity597 differed, indicating differences in the source-sink relations of these @entity599 compounds. High, but uniform, xylem sap @entity597 concentrations in April may originate from balanced @entity597 uptake by the roots, whereas high @entity462 concentrations in April, increasing with increasing height of the trunk, may originate in part from protein breakdown in the trunk. Reversal of the axial distribution of xylem sap @entity462 in late summer-early fall to higher concentrations in the lower part of the trunk than in the upper part of the trunk suggests that the upper part of the trunk becomes a sink for @entity462 as a result of the synthesis of storage proteins at this time of the year.
