Amino acids as a nitrogen source in temperate upland grasslands: the use of dual labelled (13C, 15N) glycine to test for direct uptake by dominant grasses.

Streeter, Tania C. and Bol, Roland and Bardgett, Richard D. (2000) Amino acids as a nitrogen source in temperate upland grasslands: the use of dual labelled (13C, 15N) glycine to test for direct uptake by dominant grasses. Rapid Communications in Mass Spectrometry, 14 (15). pp. 1351-1355. ISSN 0951-4198

Abstract

It is becoming increasingly apparent that soil amino acids are a principal source of nitrogen (N) for certain plants, and especially those of N-limited environments. This study of temperate upland grasslands used glycine-2-13C-15N and (15NH4)2SO4 labelling techniques to test the hypothesis that plant species which dominate unimproved semi-natural grasslands (Festuca-Agrostis-Galium) are able to utilise amino acid N for growth, whereas those plants which dominate improved grasslands (Lolium-Cynosurus), that receive regular applications of inorganic fertiliser, use inorganic N forms as their main N source. Data from field experiments confirmed that free amino acids were more abundant in unimproved than improved grassland and that glycine was the dominant amino acid type (up to 42% of total). Secondly, the injection of representative amounts of glycine-2-13C-15N (4.76 and 42.86 mM) into intact soil cores from the two grassland types provided evidence of direct uptake of glycine by plants, with both 15N and 13C being detected in plant material of both grasslands. Finally, a microcosm experiment demonstrated no preferential uptake of amino acid N by the grasses which dominate the grassland types, namely Holcus lanatus, Festuca rubra, Agrostis capillaris from the unimproved grassland, and Lolium perenne from the improved grassland. Again, both 13C and 15N were detected in all grass species suggesting uptake of intact glycine by these plants.