Abstract
Direct uptake of organic nitrogen (ON) compounds, rather than inorganic N, by plant roots has been hypothesized to constitute a significant pathway for plant nutrition. The aim of this study was to test whether tomatoes (Solanum lycopersicum cv. Huying932) can take up ON directly from the soil by using (NH4Cl)-N-15, (KNO3)-N-15, 1, 2-(C2N)-C-13-N-15-glycine labeling techniques. The C-13 and N-15 in the plants increased significantly indicating that a portion of the glycine-N was taken up in the form of intact amino acids by the tomatoes within 48 h after injection into the soil. Regression analysis of excess C-13 against excess N-15 showed that approximately 21% of the supplied glycine-N was taken up intact by the tomatoes. Atom% excesses of N-15 and C-13 in the roots were higher than in any shoots. Results also indicated rapid turnover of amino acids (e.g., glycine) by soil microorganisms, and the poor competitive ability of tomatoes in absorbing amino acids from the soil solution. This implies that tomatoes can take up ON in an intact form from the soil despite the rapid turnover of organic N usually found under such conditions. Given the influence of climatic change and N pollution, further studies investigating the functional ecological implications of ON in horticultural ecosystems are warranted. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
