Comprehensive analysis of fresh tea (Camellia sinensis cv. Lingtou Dancong) leaf quality under different nitrogen fertilization regimes.

• Nitrogen application affects tea flavor components. • High nitrogen levels increase polyphenols and amino acids, but decrease catechins. • Chlorophyll, caffeine, and theanine accumulate with nitrogen application. • Linalool and cis -linalool oxide are key compounds for tea aroma. Our study investigated the impact of nitrogen fertilization at 0, 150, 300, and 450 kg/ha on the non-volatile and volatile substances, as well as gene expression in fresh leaves from Lingtou tea plants. We found that applying nitrogen at 450 kg/ha notably increased total polyphenols (TPs) and free amino acids (AAs) while decreasing the TP to AA ratio (TP/AA) and total catechins (TC) contents. Chlorophyll, caffeine (CAF) and theanine accumulated to a greater extent with nitrogen application rates of 150, 300, and 450 kg/ha, respectively, six substances – TP, CAF, TC, theanine, epigallocatechin (EGC), and AA – as key contributors to the taste quality of LTDC. Additionally, five substances with variable importance in projections (VIP) ≥ 1 and odor activation values (OAV) ≥ 1, notably linalool and cis -linalool oxide (furanoid), significantly contributed to the tea's overall aroma. Furthermore, applying 300 kg/ha nitrogen upregulated the dihydroflavonol reductase (DFR)gene, likely causing catechin decrease. [ABSTRACT FROM AUTHOR]