Contents of free amino acids in Scots pine needles from field sites with different levels of nitrogen deposition

The response of pine stands in areas with three different levels of nitrogen deposition was analysed on samples of the current year's needles. Each test area was subdivided into five test sites. Clear changes in the amounts of amino acids in relation to the nitrogen content of pine needles were found. Analyses were mainly focused on the amino acids glutamate (Glu), glutarnine (Gin) and those forming the urea cycle. The concentration of Gin increased significantly with response to increasing needle nitrogen content. Arginine (Arg) accumulated dramatically (up to 100-fold) at high levels of needle nitrogen, but had the highest variation within the test sites. Ornithine (Orn) showed an increase only if the needle nitrogen content was very high. No clear relationship found in the case of Glu. Glutarnine and Arg are useful bioindicators of nitrogen pollution in pine stands.