The effect of liming on the soluble nitrogen pool in Norway spruce (Picea abies) exposed to high loads of nitrogen

During the growing seasons 1994, 1995 and 1996 the effects of liming of the forest soil on the pools of total soluble non-protein nitrogen (TSNN) in spruce trees (Picea abies (L.) Karst) was examined at a field site ('Hoglwald', Germany) exposed to high loads of atmospheric nitrogen. For this purpose TSNN contents of fine roots, needles (current and previous year), twig phloem and xylem and toot phloem and xylem of spruce trees grown at a plot supplied with 4000 kg calcium magnesium carbonate per ha in March 1994 were compared to untreated control trees. Liming resulted in a transient decrease in TSNN contents in fine roots, root phloem, previous year's needles, and shoot xylem that was most pronounced during the second growing season after liming and that ceased during the third growing season (1996). The observed decrease in TSNN contents in 1995 is attributed to a decrease in ammonium availability that was observed at the field site studied. The reincrease in TSNN contents in the subsequent year is supposed to be a result of changes in the regulation of pedospheric nitrogen uptake that allows the trees to adapt nitrogen absorption to their demand.