Free Amino Acids in Grand Fir Needles and the Effects of Different Forms of Foliar-applied Nitrogen

Abstract

Needles of grand fir, Abiesgrandis (Dougl.) Lindl., were analyzed to determine: (1) how various forms of nitrogen fertilizer affect amino acid composition, and (2) whether amino acids in the needles differ from those in stem bark (determined in a previous study). Young grand fir were grown in a shadehouse and free amino acids were analyzed four times from May to August, using thin-layer electrophoresis and chromatography. The effects of foliar-applied nitrogen fertilizer on needle amino acids depended on the form of nitrogen. Urea or ammonium nitrate promoted large increases in arginine, glutamine, alanine, lysine, and γ-amino butyric acid, whereas calcium nitrate caused smaller increases. The occurrence of several trace amino acids also varied with the form of nitrogen. Comparison of needle amino acids with those in the stem of unfertilized trees revealed that levels of total amino nitrogen, arginine, glutamic acid, and glutamine were much greater in the stem bark than in the needles, but levels of γ-amino butyric acid and alanine were higher in needles. Traces of aspartic acid, ornithine, and tyrosine were found in the needles, but not in the stem.