Black tea is widely consumed worldwide, and its characteristic taste and color result from fermentation, where polyphenols are enzymatically oxidized to generate major pigments, including theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). This study investigated the effects of increased oxygen treatment during fermentation on the flavor attributes and chemical properties of Congou black tea. Fresh tea leaves (variety “Fuyun 6”) were subjected to four oxygen treatments: 0 h (CK), 1 h (TY-1h), 2 h (TY-2h), and 3 h (TY-3h), with oxygen supplied at 8.0 L/min. Sensory evaluation revealed that oxygen-treated samples exhibited tighter and deeper-colored leaves, a redder liquor, fuller taste, and a sweeter fragrance compared with CK. Chromatic analysis showed significant increases in redness (a*) and luminance (L*), alongside reduced yellowness (b*), indicating enhanced liquor color. Chemical analyses demonstrated elevated levels of TFs, TRs, and TBs in oxygen treatments, with TRs showing the most pronounced increase. Non-targeted metabolomics identified 2318 non-volatile and 761 volatile metabolites, highlighting upregulated flavonoids, phenolic acids, and lipids, and downregulated catechins and tannins, which collectively contributed to improved taste and aroma. Optimal results were achieved with 2–3 h of oxygen treatment, balancing pigment formation and sensory quality. These findings can provide a scientific basis for optimizing oxygen conditions in black tea fermentation to improve product quality.

This study systematically investigated the application effects of exogenous enzymes (tannase/papain) during black tea fermentation, aiming to optimize flavor. Tannase treatment significantly reduced astringent substances like tea polyphenols and enhanced 11 metabolites, including Myricetin-3-O-arabinoside, thereby effectively enhancing fruity and sweet aromas. Papain treatment increased free amino acids and accumulated Myricetin-3-O-arabinoside and Vitexin-7-O-glucoside, significantly enhancing umami and floral flavors. Both enzyme treatments increased the odor activity value (OAV) of key aroma compounds such as (Z)-3-Hexen-1-ol and 1-Hexanol. Molecular docking revealed that hydrophobic interactions and hydrogen bonding are the key driving forces for aroma compound binding, OR5M3 and OR1A1 are key olfactory receptors for black tea aroma perception, and Benzene, n-butyl- was identified as a key aroma compound for the studied receptors. Overall, exogenous enzyme technology significantly changed the flavor of traditional black tea by reducing bitterness and astringency, as well as enhancing sweetness and floral aroma.

To investigate the effects of intercropping green manure on the tea plantation ecosystem, this study was conducted using 40-year-old Camellia sinensis cv. “Fuding Dabai” tea plants at the Tea Experimental Base of the Jiangxi Institute of Cash Crops. Four treatments were established: clean tillage (CK), tea intercropped with ryegrass (Lolium perenne, TRG), tea intercropped with rapeseed (Brassica napus, TRP), and tea intercropped with alfalfa (Medicago sativa, TAL). The study systematically evaluated the effects of green manure on tea yield, soil nutrient content, enzyme activity, and microbial community structure. The results showed that intercropping with green manure significantly increased the bud density, hundred-bud weight, and yield of tea in spring, summer, and autumn, with the TAL treatment showing the best overall performance. In terms of soil physicochemical properties, green manure treatments significantly improved soil organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium contents, with TRP and TAL showing the most pronounced improvements. Enzyme activity analysis indicated that the TRP treatment significantly enhanced the activities of amylase, urease, and invertase. High-throughput sequencing results revealed that green manure treatments significantly increased both the number of bacterial and fungal OTUs (Operational Taxonomic Units) and alpha diversity indices. The TAL and TRP treatments showed superior performance in terms of Shannon, Chao, and ACE indices compared to CK. Principal coordinate analysis (PCoA) indicated that green manure had a greater influence on fungal community structure than on bacterial structure. Correlation analysis demonstrated that dominant microbial taxa were significantly associated with soil nitrogen, phosphorus, and potassium levels, suggesting that green manure modulates microbial community composition by improving soil nutrient status. Intercropping green manure significantly increased tea yield and soil quality compared with clean tillage. Alfalfa intercropping (TAL) increased tea yield by 49.61%, 40.88%, and 43.79% in spring, summer, and autumn, respectively, compared with the control. Soil organic matter and total nitrogen under TAL were 29.02% and 15.67% higher than the control, while rapeseed intercropping (TRP) increased available phosphorus by 186%. TAL and TRP also enhanced microbial diversity, with bacterial Shannon index values 14.11% and 11.25% higher than the control. These results indicate that alfalfa intercropping is the most effective green manure practice for improving tea plantation productivity and soil ecology.

Black tea is a globally popular beverage, whose unique flavor and color are attributed to the fer-mentation process, during which polyphenols undergo enzymatic oxidation to form key pigments such as theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). This study investigated the effects of increased oxygen treatment during fermentation on the sensory and chemical qualities of Congou black tea. Fresh tea leaves (variety "Fuyun 6") were subjected to four oxygen treatments: 0 h (CK), 1 h (TY-1h), 2 h (TY-2h), and 3 h (TY-3h), with oxygen supplied at 8.0 L/min. Sensory evaluation revealed that oxygen-treated samples exhibited tighter and darker appearances, redder liquor, thicker taste, and sweeter aroma compared to CK. Chromatic analysis showed significant increases in redness (a*) and luminance (L*), alongside reduced yellowness (b*), indicating en-hanced liquor color. Chemical analyses demonstrated elevated levels of TFs, TRs, and TBs in oxygen treatments, with TRs showing the most pronounced increase. Non-targeted metabolomics identified 2318 non-volatile and 761 volatile metabolites, highlighting upregulated flavonoids, phenolic acids, and lipids, and downregulated catechins and tannins, which collectively contributed to improved taste and aroma. Optimal results were achieved with 2–3 h of oxygen treatment, balancing pigment formation and sensory quality. These findings can provide a scientific basis for optimizing oxygen conditions in black tea fermentation to improve product quality.

Long-term monoculture in tea plantations leads to soil fertility decline and microbial community degradation, restricting tea growth and ecosystem function. To explore sustainable management strategies, we conducted a field experiment in a 40-year-old Camellia sinensis cv. “Fuding Dabai” plantation with intercropping of three leguminous green manures: alfalfa (TAL), hairy vetch (THV), and Chinese milk vetch (TMV). All treatments significantly improved bud density, hundred-bud weight, and yield, with TAL and THV increasing spring and summer yields by more than 40% and THV achieving the highest autumn yield (650.17 kg·hm ⁻² ). Soil fertility was markedly enhanced, particularly under THV, with notable increases in organic matter, nitrogen, and available phosphorus. Enzyme activities responded differentially: TAL enhanced urease and sucrase, TMV promoted amylase and phosphatase, and THV increased catalase activity. High-throughput sequencing revealed shifts in bacterial ( Pseudomonadota , Planctomycetota ) and fungal ( Ascomycota , Basidiomycota ) communities, with THV showing the highest bacterial OTU richness. Functional predictions indicated enhanced microbial potential in carbon, nitrogen, and phosphorus cycling, especially under THV. Overall, leguminous green manure intercropping improved soil fertility, enzyme activity, and microbial communities, thereby enhancing tea yield, with hairy vetch showing the most consistent benefits. These findings provide insights into microbial-mediated soil improvement and offer a sustainable pathway for managing aging tea plantations.

Tea quality is largely determined by the accumulation of specialized metabolites in fresh leaves, yet the effects of the propagation method on tea quality and its belowground ecological basis remain insufficiently understood. In this study, sexually propagated (SR) and asexually propagated (AR) tea plants were compared by integrating soil physicochemical analysis, leaf quality and physiological measurements, widely targeted metabolomics, and rhizosphere metagenomic profiling. Compared with AR, SR plants exhibited more favorable rhizosphere nutrient conditions, with soil organic matter, total nitrogen, alkali-hydrolyzable nitrogen, and available phosphorus increasing by 23.1%, 18.2%, 27.8%, and 161.5%, respectively, although available potassium decreased by 24.4%. SR leaves also contained higher dry matter, tea polyphenol, and soluble sugar contents, which increased by 11.5%, 58.8%, and 8.6%, respectively. In addition, superoxide dismutase, peroxidase, and indole-3-acetic acid oxidase activities were 30.4%, 92.0%, and 21.7% higher under SR, whereas hydrogen peroxide content remained unchanged. Metabolomic profiling revealed marked differences in leaf metabolic composition between the two propagation types, with differentially accumulated metabolites mainly enriched in flavonoid biosynthesis, phenolic acid metabolism, caffeine metabolism, carotenoid biosynthesis, plant hormone signaling, and α-linolenic acid metabolism. Rhizosphere metagenomic analysis further showed that SR was characterized by higher relative abundances of Actinomycetota, Pseudomonadota, Planctomycetota, Alphaproteobacteria, and Streptomycetales, together with distinct microbial functional profiles related to glycolysis, the tricarboxylic acid cycle, and pyruvate metabolism. Significant correlations were identified between several SR-enriched microbial taxa and quality-related metabolites, particularly flavonoids and phenolic acids. Overall, under the present field conditions, sexual propagation was more favorable than asexual propagation for tea quality formation, as reflected by improved nitrogen and phosphorus availability, greater accumulation of quality-related metabolites, higher antioxidant enzyme activities, and distinct rhizosphere microbial carbon-metabolic potential. These findings provide an integrated soil–microbiome–metabolome perspective for understanding propagation-related differences in tea quality.