A contribution to understanding the internal nitrogen budget of beech (Fagus sylvatica L.)

Summary The seasonal variation in the total nitrogen content of the xylem sap of the lower trunk section was investigated for two middle aged beech tree stands in northern Hessen each containing 130 trees. In addition seasonal changes in the percentage of nitrate in the total nitrogen content are described. The median values of the total nitrogen content of the xylem sap during the spring mobilization period reached 175 and 250 mg/l. During the summer about 35% of the total nitrogen in the xylem sap is in the form of nitrate. Finally, the distribution of NO₃ in the xylem sap along the trunk height was studied for two sample trees for each of the four seasons (n = 8).