Large-Scale Stable Isotope Distribution and Characteristics of Organic Tea with δ15N Signature of the Conversion Period in China.

Chinese organic tea market faces potential label misuse, but nitrogen isotope distributions relevant to its authentication remain unclear. This study used isoscapes, normal models, and pot experiments to investigate Chinese organic tea isotopes and fertilizer effects on δ15N during the conversion period. Results showed that organic tea exhibits a broad range of δ15N values from -2.0‰ to 5.5‰ (P5-P95) with a mean of 1.8‰, with organic black tea (P25-P75) showing slightly wider δ15N than green tea. The mean δ13C, δ2H, and δ18O values were -27.1‰, -54.1‰, and 24.8‰, respectively, showing depletion over years. Pot experiments showed that chemically fertilized tea plants exhibited a significant decrease in δ15N values earlier than organically fertilized ones during the conversion period. This first large-scale survey indicates that, although δ15N alone cannot universally authenticate all organic teas, it remains a promising indicator when combined with complementary methods.