Uptake of amino acids and inorganic nitrogen by two dominant temperate grasses

Abstract The free amino acids play an important role in total nitrogen (N) absorption for plants. Most previous studies, however, only focused on the organic N uptake of glycine or several simple amino acids by plants. The purpose of this research was to quantify the uptake rate of N derived from multiple amino acids and evaluate the importance of different N forms (amino acid N and inorganic N) to plant nutrition. A range of amino acids (aspartic acid, lysine, leucine, phenylalanine, proline, valine, alanine, glutamine, isoleucine and glycine) and inorganic N (NH4+ and NO3-) with the same amount of N for each of 12 N forms were used in a short-term (3 h) 15N labeling experiment in a temperate grassland of North China. Two dominant plant species, Stipa grandis and L. chinensis, were investigated. Within 3 h, the N derived from multiple amino acids were both absorbed by S. grandis and L. chinensis, contributed about 25% and 37% to the total N uptake by two plant species, respectively. Leymus chinensis is relatively more effective in utilizing N derived from amino acids compared to S. grandis, while S. grandis takes up more inorganic N of NH4+ and NO3-. The uptake rates of N derived from multiple amino acids by S. grandis and L. chinensis differed greatly, and which have significant positive relations with soil amino acid concentrations (r2 = 0.59, P