Influence of Tea Stand Age on Leaf Biochemical Components, Mineral Elements, and Rhizosphere Soil Properties in Wuyi Rougui (Camellia sinensis (L.) Kuntze)

This study systematically investigated the effects of stand age (5, 10, 20, and 40 years) on the biochemical components, mineral element accumulation in leaves, and rhizosphere soil properties of the tea shrub Camellia sinensis (L.) Kuntze cv. Wuyi Rougui. Analyses were performed on dried and ground leaf samples, and rhizosphere soil was collected from multiple independent plots per age group (n = 3). The results showed that the contents of tea polyphenols, water extract, caffeine, total flavonoids, and free amino acids in leaves initially increased, peaked at 10 or 20 years, and then decreased with increasing stand age. Soluble sugar content was highest at 5 years. The accumulation patterns of leaf mineral elements (Mg, Mn, K, Na, Fe, Zn, Cu, Ca) were also significantly influenced by stand age. Soil physicochemical properties (pH, total nitrogen, available phosphorus, organic matter, etc.) and enzyme activities (protease, polyphenol oxidase, urease, sucrase) exhibited distinct trends, i.e., pH decreased initially and then increased, while organic matter content increased with stand age. Principal component analysis (PCA) revealed that tea quality indicators, mineral elements, and soil properties clearly separated the 5- and 40-year groups, while the 10- and 20-year groups were closer. Pearson correlation analysis indicated significant positive correlations between leaf total flavonoids and soil ammonium nitrogen (r = 0.82, p < 0.01), and negative correlations between leaf soluble sugar and soil ammonium nitrogen (r = −0.75, p < 0.05). In summary, stand age was associated with systematic changes in both tea leaf composition and soil environment, suggesting that soil nutrient availability and enzyme activity may modulate tea quality formation. These findings provide a theoretical basis for age-specific soil and nutrient management in tea plantations.