## 1 Introduction  
Phenolic and volatile compounds are important secondary metabolites in wine grapes that are extracted during the maceration and fermentation processes, providing color and aroma to the wine. Generally, phenolic metabolites in wine grapes originate from the flavonoid metabolic pathway, while aroma metabolites are derived from three distinct metabolic pathways. These pathways include the lipoxygenase pathway, which produces C6/C9 compounds and volatile thiol precursors; the plastidic methylerythntol phosphate and cytosolic mevalonic acid pathways, which generate monoterepenes and C13-norisoprenoids; and the phenylalanine pathway, which produces aromatic compounds such as benzenoids and phenylproponioids [1]. These secondary metabolic pathways are influenced by a range of biotic and abiotic factors, including sunlight, temperature, precipitation, microbial diseases, and insect damage [2; 3; 4]. In order to enhance grape growth conditions, grape growers around the world implement numerous agronomic techniques, including leaf removal, canopy training systems, foliar fertilization, deficit irrigation, and inter-row planting [5; 6; 7]. These practices ultimately alter the secondary metabolism of grape berries, leading to an improvement in the quality of the colour and aroma. Cluster-zone leaf removal, also known as basal leaf removal, is a viticulture practice aimed at improving the microclimate of grapevines. This practice aims to enhance air circulation, increase cluster exposure, reduce pests and diseases, and improve berry quality. Previous studies have indicated that the effects of cluster-zone leaf removal on grape-berry ripening and phenolic content are inconsistent, possibly due to varietal and treatment-period differences. Investigations of Sauvignon Blanc grapes demonstrated that removing leaves around veraison (two weeks before, during, and two weeks after) may lead to a decrease in levels of both titratable acid (TA) and total soluble solids (TSS) in grape berries [8]. Conversely, removing leaves at an earlier phenological stage (15 days before and after flowering) did not significantly affect either TA or TSS levels in ripe grape berries [9; 10]. Cluster-zone leaf removal of Pinot Noir at different stages, including flowering, pea grain size, and cluster closure, has been shown to promote the accumulation of anthocyanins and flavonols. Furthermore, early leaf removal has been found to result in higher anthocyanin levels [11]. Similar results have been observed in leaf-removal treatments of Cabernet Sauvignon grapes performed at the beginning and end of veraison [5; 12]. However, for Merlot grapes, leaf removal before and after flowering did not result in any discernible changes in the levels of anthocyanins and tannins [13]. Several studies have demonstrated the diverse effects of cluster-zone leaf removal on grape volatile compounds, with the effects varying depending on the grape variety, climate, treatment stage, and intensity. Most of these studies have indicated that the removal of leaves has the effect of promoting the synthesis of monoterenes, specifically \(a\)-terpineol and linalool, and their oxidised derivatives [10; 11; 14]. One study observed an increase in the total amount of monoterenes in the group with 50% leaf removal during veraison, while no significant difference was observed in the group with 100% defoliation [8]. Furthermore, leaf removal during the pepper-corn-size stage and veraison resulted in a reduction in the total tempering content in an intensely light, dry-hot climate [15], indicating that overexposure could have a negative impact on tempering accumulation. A number of studies have indicated that leaf removal from the cluster zone can lead to increased levels of norisoprenoids [11; 14; 16]. This is thought to be linked to increased synthesis of carotenoids [10]. Nevertheless, two studies on Cabernet Sauvignon grapes demonstrate that the \(\beta\)-damascenone levels were markedly lower in the defoliated group than in the control group [15].