Abstract
<title>Abstract</title> <p> Aim Foliar nitrogen (N) application is an effective approach in viticulture to improve grapevine N status and grape quality parameters. However, it is not well understood whether foliar-applied N also affects belowground metabolic processes such as root exudation. The present study investigated the effects of repeated foliar N application on root amino acid (AA) concentrations and AA exudation of <italic>Vitis vinifera</italic> L. cv. Riesling under semi-field conditions. Methods Grapevines received weekly foliar applications with 1% or 2% carbamide and methylene carbamide and were analysed at three independent sampling dates. Root exudates were collected using a semi-hydroponic collection system, and AAs in root tissue and exudates were quantified by ion-exchange chromatography with post-column ninhydrin derivatization. Multivariate treatment effects were evaluated using PERMANOVA and redundancy analysis (RDA) based on both log1p-transformed concentrations and centered log-ratio (CLR)-transformed compositional profiles. Results Foliar N application significantly increased leaf N concentrations, root N concentrations, total root AA concentrations, and total AA exudation rates across all sampling dates. Magnitude-based multivariate analyses revealed consistent treatment-associated restructuring of exudation profiles across sampling dates, primarily driven by alanine, γ-aminobutyric acid, glutamic acid and valine. In contrast, compositional analyses detected significant treatment-associated restructuring only during the first sampling date where glutamine and cysteine were associated with foliar N application, whereas β-aminoisobutyric acid, histidine, and serine aligned more strongly with control vines. Conclusion Results demonstrate that foliar-applied N can substantially alter grapevine AA exudation dynamics through both increased exudation magnitude and transient shifts in exudate composition. These findings indicate that foliar N supply influences grapevine belowground AA release under standardized semi-hydroponic collection conditions, suggesting potential changes in rhizosphere substrate supply without intentional soil N fertilisation during the experimental treatment period. </p>