Metabolomics Reveal That the High Application of Phosphorus and Potassium in Tea Plantation Inhibited Amino-Acid Accumulation but Promoted Metabolism of Flavonoid

Abstract

As leaf-harvest plants, tea trees show unique nutrient requirements, different from those of corn and other field crops. However, the effects of nitrogen (N), phosphorus (P), and potassium (K) application on the accumulation of quality-related compounds and the mechanisms underlying how nutrients affect tea-leaf metabolism have not been well elucidated. Here, fertilizers with different N, P, K ratios were applied to tea plants in pot experiments, and metabolomics based on gas chromatography-mass spectrometry (GC-MS) combined with multivariate statistical and quantitative detections were conducted to assess the responses of quality-related compounds to NPK in tea leaves. An increased proportion of P and K was beneficial for the accumulation of carbohydrates and catechins in shoots, although the total carbon content did not increase significantly. In contrast, a high proportion of P and K input reduced the relative chlorophyll content in shoots, and the contents of free amino acids such as theanine and glutamic acid negatively correlated with P and K nutrient content. Moreover, the metabolism of malic acid in the tricarboxylic acid cycle was highly promoted by increasing the application of P and K. These results validate our suggestion that the application of high amounts of P and K in tea plantations induces the biased reallocation of photosynthates and carbohydrates to the catechin pathway by promoting malic acid metabolism in young tea shoots, which further affects tea quality. The results of this study provide theoretical ground for tea quality improvement by optimizing fertilization strategies.