To investigate the effect of light intensity and temperature on the biosynthesis and accumulation of quality-related metabolites, field grown tea plants were shaded by Black Net and Nano-insulating Film (with additional 2–4°C cooling effect) with un-shaded plants as a control. Young shoots were subjected to UPLC-Q-TOF MS followed by multivariate statistical analysis. Most flavonoid metabolites (mainly flavan-3-ols, flavonols and their glycosides) decreased significantly in the shading treatments, while the contents of chlorophyll, β-carotene, neoxanthin and free amino acids, caffeine, benzoic acid derivatives and phenylpropanoids increased. Comparison between two shading treatments indicated that the lower temperature under Nano shading decreased flavonols and their glycosides but increased accumulation of flavan-3-ols and proanthocyanidins. The comparison also showed a greater effect of temperature on galloylation of catechins than light intensity. Taken together, there might be competition for substrates between the up- and down-stream branches of the phenylpropanoid/flavonoid pathway, which was influenced by light intensity and temperature.

Tea plants are well-adapted to NH(4+)-rich environments by exhibiting a high capacity for NH4+ assimilation in their roots, reflected in strongly increased key enzyme activities and improved carbohydrate status. The poor plant growth with NO3- was largely associated with inefficient absorption of this N source. Decreased growth caused by inappropriate external pH corresponded well with the declining absorption of nitrogen.

The concentrations of free amino acids (AA) and polyphenols (PP) are important determinants of green tea quality. Levels of AA and PP are governed interactively by nitrogen (N) supply and carbon (C) status, so the impact of C/N allocation on green tea quality was investigated in saplings cultivated hydroponically with 0.3, 0.75, 1.5 or 4.5 mmol l(-1) N. Activities of glutamine synthetase (GS), phenylalanine ammonia lyase (PAL), and phosphoenolpyruvate carboxylase (PEPC) were determined, as were concentrations of AA, PP and soluble sugars. Concentrations of AA increased with increasing N supply, and the AA profile was shifted towards AA characterised by low C/N ratios (arginine, glutamine) and away from theanine, the unique non-protein AA that is abundant in Camellia sinensis. High N supply significantly reduced the concentrations of PP in young shoots, and was accompanied by lower levels of carbohydrates (soluble sugars). Analysis of the C and N status and selected enzyme activities, combined with path coefficient analysis of variables associated with C and N metabolism, demonstrated increasing deviation of C flux to AA under abundant N supply. Accumulation of AA and PP depended strongly on N status, and the balance shifted toward increasing synthesis of AA associated with enhanced growth, while investment of C in secondary metabolites did not change proportionally under the condition of ample N supply.

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The sensory quality of green tea changes greatly within a single spring season, but the mechanism is not clearly elucidated. Young shoots of the early, middle, and late spring season were subjected to metabolite profiling using gas chromatography-time-of-flight mass spectrometry (TOF/MS) and ultraperformance liquid chromatography-quadrupole-TOF/MS. Multivariate analyses revealed largely different metabolite phenotypes in young shoots among different periods. The contents of amino acids decreased, whereas carbohydrates, flavonoids and their glycosides, tricarboxylic acid cycle, and photorespiration pathways were strongly reinforced in the late spring season, which were well reflected in the sensory quality of made teas. Metabolomic analyses further demonstrated distinct variations of metabolite phenotypes in mature leaves. The results suggested that the fluctuation of green tea quality in the spring season was caused by changes of metabolite phenotypes in young shoots, which was likely related to the remobilization of carbon and nitrogen reserves from mature leaves.

Properties of leaf and infusion colours, chemical components and volatile flavour compounds of Longjing teas and their correlation with perceived quality score given by tea-tasting panel were analysed. The scores for appearance, infused leaves and for the Total Quality Score (TQS) negatively correlated with concentrations of chlorophyll-a (Chl-a), Chl-b and total chlorophyll (r = )0.723 to )0.846, P < 0.01). The perceived taste score positively correlated with the concentration of total free amino acid (r = 0.527, P < 0.05) and theanine (r = 0.511, P < 0.05), whereas the TQS positively correlated with total free amino acid (r = 0.533). The volatile composition and their quantities varied widely among Longjing tea samples. (E)-geraniol, linalool, hexanal, pentanal, heptanal, nonanal and jasmone were prevailing volatile compounds detected in all samples. Principal component analysis (PCA) screened twelve principal components with the first three explaining 18.82%, 15.31% and 11.83% of the total variance respectively. The concentrations of total free amino acids, pentanal and epigallocatechin gallate were with the highest component score coefficients for the first three principal components respectively. Regression analysis upon the twelve principal components formulated a prediction model on the TQS with 77.0% probability.

BackgroundNitrogen (N) plays an important role in the formation of tea quality-related compounds, like amino acids and flavor/aroma origin compounds. Lipids, which have been reported to be affected by N deficiency, are precursors to the generation of flavor/aroma origin compounds in tea plant. However, there is no literature about the lipid profiles of tea plant affected by N fertilization. Hence, we hypothesize that the biosynthesis of flavor-related compounds in tea was affected by N through its regulation of lipid metabolism.ResultsIn this study, mature leaves and new shoots of tea plant grown under three N levels at the rates of 0, 285 and 474 kg/ha were applied for ultra-performance liquid chromatography-mass spectrometry (UPLC/MS) based lipidomic analysis. Totally, 178 lipid species were identified. The results showed that the composition of lipid compounds in mature leaves and new shoots varied dramatically, which was also affected by N levels. The higher content of the storage lipid TAG and higher carbon (C)/N ratio in mature leaves than that of new shoots in tea plants grown under low N level (0 kg/ha) suggested that tea plants could remobilize the C stored in TAG to maintain their C/N balance and help to improve the quality of tea. N fertilization resulted in a higher content of the compounds 36:6 MGDG and 36:6 DGDG. Since these compounds contain linolenic acid (18:3), a precursor to the formation of aroma origin compounds, we suggested their increase could contribute to the quality of tea.ConclusionsTaken together, the present work indicated that appropriate application of N fertilizer could balance the lipid metabolism and the formation of flavor/aroma origin compounds, which help to improve the quality of tea. Moreover, excess N fertilization might deteriorate the aroma quality of made tea due to increases of precursors leading to grassy odor.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1111-6) contains supplementary material, which is available to authorized users.