Seasonal Changes in Nitrogen Metabolism of Spruce Needles ( Picea abies (L.) Karst.) as Affected by Water Stress and Ambient Air Pollutants

Abstract

Summary Sixteen-year-old spruce trees ( Pice abies ) enclosed in their natural habitat in open-top chambers with charcoal-filtered and non-filtered air were studied from 1988 -1991 to evaluate the long-term impact of ambient air pollutants on needle nitrogen metabolism (contents of soluble protein and amino acids and activities of glutamine synthetase and glutamate dehydrogenase). Investigation of diurnal variations in soluble amino acid contents revealed a maximum of glutamate, serine and glycine and a minimum of aspartate at noon. The typical ontogenetic curves in nitrogen metabolism of young needles from flushing until October of the next year consisted of distinct phases: (1) within the first vegetation period a strong increase in needle protein and enzyme activities, (2) during winter a decrease in amino acid content, (3) in springtime a maximum in amino acid content, (4) in early summer a temporary decrease in protein content, and (5) in late summer an increase in arginine content in some trees. Beside seasonal changes, levels of the parameters were found to vary strongly between trees and over the four years of investigation. No relationship could be found between parameters of needle nitrogen metabolism and soil nitrate or ammonium concentrations. However, there was a relationship between the soil water potential and protein content (r = 0.8) and glutamine synthetase activity (r = 0.6) in the needles, indicating that both parameters increase under conditions of water stress. These physiological alterations are supposed to be based on stress-induced translocation of nitrogen from the old to the young foliage. Trees kept in chambers with non-filtered air showed higher levels of protein and glutamine synthetase activity than trees of the clean air treatment. However, the edaphic data indicate this hardly to be an effect of ambient ozone levels, but of differences in soil water status between the two variants.