NITROGEN DISTRIBUTION IN YOUNG NORWAY SPRUCE (PICEA-ABIES) TREES AS AFFECTED BY PEDOSPHERIC NITROGEN SUPPLY

In numerous locations in Europe spruce trees are exposed to high loads of nitrogen. The present study was performed to characterize the dist ribution of nitrogen compounds under these conditions. For this purpos e Norway spruce (Picea abies [L.] Karst.) trees were cultivated under close-to-natural conditions of a forest understory in soil from an app arently nitrogen-limited field site in the Black Forest either with, o r without supplementation of nitrogen as ammonium nitrate. After 11 an d 20 months, growth, total nitrogen contents of the biomass, and total soluble non-proteinogenic nitrogen compounds (TSNN, i.e. nitrate, amm onium, soluble proteinogenic and non-proteinogenic amino compounds) in needles, xylem sap and phloem exudate were analysed. After 20 months of growth, N-fertilization had slightly enhanced the biomass of curren t-, but not of 1-year-old shoots. At both harvests, total N-content of 1-year-old needles was increased by N-fertilization, whereas current- year needles were not significantly affected. By contrast, TSNN was el evated by N-fertilization in both current-year and 1-year-old needles. The increase in TSNN was mainly attributed to an accumulation of argi nine. Xylem sap analysis showed that the increase in TSNN of the needl es was a consequence of enhanced nitrogen assimilation of the roots ra ther than the shoot. Since also TSNN in phloem exudates was enhanced, it appears that N-fertilization elevates the cycling pool of amino com pounds in young Norway spruce trees. However, this pool seems to be su bject to metabolic interconversion, since mainly glutamine and asparta te are transported in the xylem from the roots to the shoot, but argin ine accumulated in the needles and the phloem.