Inter-Row Reflective Film Mulching Revealed the Regulation of Ground-Reflected Light on the Grape Fruit Flavoromics

Inter-row mulching with reflective film (RF) has been increasingly adopted in cool-climate vineyards to improve light availability and promote grape ripening. This study investigated the effects of ground-reflected light on the flavoromic profiles of wine grape berries (Vitis vinifera L.) over two consecutive vintages (2020–2021) in the Beijing Fangshan region of Eastern China, an area characterized by high precipitation and limited sunlight during ripening. Physicochemical analyses showed that RF treatment significantly increased total soluble solids (TSS) and decreased titratable acidity (TA) at harvest. Targeted metabolomic analyses using HPLC–MS and GC–MS identified 21 flavonoids and 35 volatile compounds responsive to altered light conditions. RF treatment markedly enhanced the accumulation of anthocyanins and flavonols, especially malvidin-based derivatives, and increased terpene and norisoprenoid concentrations, while C6/C9 compounds were more abundant in control berries. Multivariate analysis revealed that PC1 was mainly associated with anthocyanin accumulation, clearly separating RF-treated samples, whereas PC2 reflected differences in flavonols and flavan-3-ols, with higher flavonols under RF and higher skin- and seed-derived flavan-3-ols in controls. Overall, these findings demonstrate that ground-reflected light plays a critical role in modulating grape flavor composition and provides practical guidance for improving fruit quality in suboptimal climatic regions.