The study site was located in a tea plantation in Fuliang County, Jingdezhen City, Jiangxi Province (E 116°57′--117°42′, N 28°44′--29°56′). The study area experiences a subtropical monsoon climate with distinct seasons and concurrent rain and heat. Precipitation is concentrated in spring and summer, while autumn and winter are mild. The annual average temperature is 17.36°C, with historical extreme maximum temperatures exceeding 40°C and extreme minimum temperatures below -5°C. The average annual precipitation is 1763.5 mm, unevenly distributed in time and space, with the rainy season from April to June accounting for about 46% of the annual total. The terrain is predominantly low mountains and hills, with layered tea terraces, significant diurnal temperature variation, and high air humidity. The soil is primarily red and yellow earth, rich in organic matter and minerals. With a forest coverage rate exceeding 80% and minimal industrial pollution, it is a typical high-quality tea production area, providing an ideal environment for premium tea growth. The experiment was conducted from March to April 2025, encompassing five different cultivation modes, whose basic profiles are shown in Table 1.

Microclimate data were collected using miniature environmental monitoring systems (ME40, Beijing Shiyu Tong Technology Co., Ltd.). One monitoring device was installed in each of the HT, HTF, and PT tea gardens to continuously track parameters such as air temperature, air humidity, total solar radiation, and topsoil moisture content at the tea canopy level. Data were recorded at 10-minute intervals. After quality control processing, daily average values were calculated. The mean values and standard deviations of each meteorological factor during the entire experimental period (March to April 2025) were compiled for subsequent analysis.

The dynamic trends of various morphological indicators of tea buds were generally consistent across different cultivation modes (Figure 1). Tea bud length and number continuously increased throughout the sprouting process (P < 0.05; Figures 1A, C; Supplementary Table S3). The relative growth for bud length was 20% and 106% during the early-to-middle and middle-to-late stages, respectively. The corresponding relative growth for bud number were 74% and 44%. In contrast, bud width gradually decreased (Figure 1B; Supplementary Table S3), with a significant reduction of -21% during the early-to-middle stage (P < 0.05) and no significant change thereafter (P > 0.05). Bud size overall showed an initial decrease (relative change: -24%) followed by an increase (relative change: 92%) (P < 0.05; Figure 1D; Supplementary Table S3).

Furthermore, the growth rates for tea bud length, width, and size during the middle-to-late stage were significantly higher than those during the early-to-middle stage (P < 0.05, Figure 2), whereas the growth rate for bud number did not differ significantly between the two stages (P > 0.05, Figure 2). This pattern was consistent across most cultivation modes (Supplementary Figure S5). Across all cultivation modes, the growth rates for length and number were consistently positive, whereas the rate for width remained negative. The growth rate for bud size shifted from negative to positive. These patterns of growth rates corroborate the consistent overall developmental trends described above (Figure 1; Supplementary Figure S5).

Cultivation mode had no significant effect on tea bud length at any of the three observed sprouting stages (P > 0.05; Figure 3A). In contrast, it exhibited a significant regulatory effect on bud width and size (P < 0.05; Figures 3B, D). Specifically, Hilly Tea Monoculture (HT) and Plain Tea-Soybean Intercropping (PTS) maintained larger bud width and size throughout the sprouting period, with their average values across stages being significantly higher by 24%–109% compared to other modes (P < 0.05; Figures 3B, D). The response of bud number to cultivation mode varied depending on the sprouting stage (Figure 3C). No cultivation mode showed a clear advantage at the early stage. However, by the middle and late stages, Plain Tea Monoculture (PT) and Plain Tea-Forest Intercropping (PTF) supported significantly higher densities than other modes, with this advantage further increasing to 72% at the late stage (P < 0.05; Figure 3C).

Regarding chemical quality, cultivation mode significantly affected all three chemical indicators (P < 0.05; Figures 4A–C). Specifically, PT and PTS were associated with a “refreshing” quality profile, characterized by the highest free amino acid content (4.0%; Figure 4A) and the lowest tea polyphenol content and polyphenol-to-amino acid ratio (16.4% and 4.26; Figures 4B, C). Conversely, HT and Hilly Tea-Forest Intercropping (HTF) were linked to a “mellow and robust” profile, exhibiting the lowest free amino acid content (2.5%; Figure 4A) and the highest tea polyphenol content and polyphenol-to-amino acid ratio (18.0% and 7.51; Figures 4B, C). The chemical indicators for PTF were intermediate between these two distinct categories.

Except for its non-significant effect on bud length, cultivation mode, sprouting stage, and their interaction all had significant effects on the various tea bud morphological indicators (Figure 5; Supplementary Table S3). Specifically, the sprouting stage accounted for a substantially higher proportion of variance in bud length variation than cultivation mode did (82.9% vs. 3.5%; Figure 5A). Conversely, bud size was more sensitive to cultivation mode than to sprouting stage (66.6% vs. 19.5%; Figure 5A). The relative contributions of these two factors to bud width variation were similar (40.7% vs. 43.1%; Figure 5A). Notably, in the model for bud number, the interaction effect accounted for a greater proportion of variance (59.2%) than either factor alone (Figure 5A).

Effect size analysis revealed that cultivation mode had the smallest effect on bud length (partial ω² = 0.132), while its effects on the other three morphological indicators were similar (0.739–0.768) (Figure 5B). Sprouting stage had the largest effect on bud length (0.812), followed by its effect on bud width (0.676), and its effects on bud number and size were similar (0.341–0.349) (Figure 5B). The interaction effect was greatest on bud number (0.735), which was 2–4 times larger than its effects on the other three indicators (Figure 5B).

Cultivation mode had significant effects on the chemical and morphological indicators measured at the late sprouting stage, as well as on the overall growth rates of tea buds during the entire sprouting period (Figure 6; Supplementary Table S7). Among these, cultivation mode exerted the strongest influence on late-stage bud number and its overall growth rate (partial ω²: 0.831–0.864), followed by late-stage bud width and its growth rate (0.601–0.620). Its effects on late-stage free amino acid content and the polyphenol-to-amino acid ratio ranked third (0.508–0.534) (Figure 6A). The effect of cultivation mode on the overall growth rate of length (0.500) was greater than its effects on late-stage bud size and its overall growth rate (0.403–0.490) (Figure 6A). Late-stage bud length and tea polyphenol content were the least responsive to cultivation mode (0.360–0.397) (Figure 6A). Overall, cultivation mode had a greater effect on the composite morphological index (0.753) than on the composite growth rate index (0.699) or the composite chemical quality index (0.530) (Figure 6B).

Bud length and width were significantly positively correlated at the early sprouting stage (r = 0.58, P < 0.05) but showed no significant correlation at the middle or late stages (P > 0.05). The correlation coefficient between length and width shifted from positive to negative from the early to the late stage (P < 0.05; Figure 7A). Bud length and number were not significantly correlated at any of the three stages. Their correlation coefficient first decreased and then increased during sprouting, with the coefficients at the early and late stages both being significantly different from that at the middle stage (P < 0.05; Figure 7B). Bud width and number were significantly negatively correlated at the late stage (r = -0.81, P < 0.05), but not at the early or middle stages (P > 0.05). The correlation coefficient between width and number also declined from positive to negative from the early to the late stage (P < 0.05; Figure 7C).

Systematic correlations were observed among the chemical indicators (Figure 8): free amino acids were significantly negatively correlated with tea polyphenols (r = -0.69;P < 0.05); the negative correlation between the polyphenol-to-amino acid ratio and free amino acids (r = -0.97;P < 0.05) was stronger than its positive correlation with tea polyphenols (r = 0.81;P < 0.05). Notably, no significant correlations were detected between any chemical indicators and the tea bud morphological indicators measured at the final stage or growth rates throughout the sprouting period (Figure 8). Further analysis revealed a positive correlation between the growth rates of bud number and length (r = 0.41; P < 0.05), while the growth rate of number was negatively correlated with both the late-stage bud width (r = -0.73; P < 0.05) and the growth rate of bud size (r = -0.70; P < 0.05). The growth rate of bud size was positively correlated with the growth rates of both length (r = 0.59; P < 0.05) and width (r = 0.83; P < 0.05) (Figure 8).

As the primary harvesting target of premium teas, the dynamic morphological development of tea buds directly affects the yield of fresh leaves and is a crucial objective of tea garden agronomic management. Within the observational framework of three time points in this study, we found that despite the diversity in cultivation modes, the morphological development of tea buds exhibits an inherent conservatism: their length and number continuously increased throughout the sprouting period, width gradually decreased, while bud size showed an initial decrease followed by an increase. This overall trend remained consistent across different cultivation modes (Figure 1; Supplementary Figure S5). This consistent pattern indicates that tea bud development follows an inherent, genetically programmed blueprint (De Costa et al., 2007; Zhang et al., 2016, 2025b). However, in-depth analysis revealed significant differences in the responses of different morphological traits to external cultivation environments, uncovering the complex interaction between genetic control and agronomic plasticity.

Specifically, the development of tea bud length exhibited strong genetic constraint. This trait had an extremely high effect size for the sprouting stage (0.812) and a very low effect size for cultivation mode (0.132) (Figure 5B), indicating that its orderly elongation is a core event in the sprouting process, primarily driven by internal developmental signals, with limited scope for external cultivation regulation. In contrast, the development of tea bud width, size, and number showed higher phenotypic plasticity. Their response to cultivation mode was stronger than that of bud length (effect sizes 0.739—0.768, Figure 4A). Previous research has mostly focused on the genetic analysis of static morphology; for example, Zhang et al. (2025b) revealed key genes regulating tea bud size through digital phenotyping, GWAS, and transcriptomic analysis. Based on dynamic observations at limited time points, this study preliminarily outlines the plasticity patterns of tea bud morphological development, suggesting that width and number may be key traits responsive to cultivation regulation. This finding provides initial evidence and potential targets for considering tea bud width and number as key plastic traits for agronomic intervention, although the underlying patterns and mechanisms require further validation through higher-frequency continuous monitoring in the future.

During the early sprouting stage, tea bud length and width exhibited a significant positive correlation. Although the relationships between the other two pairs of morphological indicators did not reach statistical significance, they also showed positive associations (Figures 7A–C). This suggests that under conditions of sufficient resources in the initial sprouting phase, there is synergistic resource allocation among different morphological dimensions. As sprouting progressed, tea bud length and width, as well as width and number, showed negative correlations at the late sprouting stage, and these correlation coefficients were significantly different from those observed at the early stage (Figures 7A, C). This dynamic pattern clearly reveals a shift in tea bud developmental strategy: from synergistic growth in the early stage to a gradual shift towards competitive allocation of limited resources in the late stage between individual lateral expansion (width) and population density (number), as well as longitudinal extension (length). It is noteworthy that length and number showed no significant correlation throughout all periods (Figure 7B), while a significant positive correlation existed between the growth rates of length and number (Figure 8), suggesting a synergistic promotion between vertical elongation and population expansion. This finding aligns well with the classic plant size–density relationship theory in ecology and the dynamic optimization theory of plant growth (Callaway and Walker, 1997; Iwasa, 2000), and systematically verifies for the first time the existence of such a trade-off mechanism during tea bud sprouting. This intrinsic trade-off relationship provides a key mechanistic perspective for understanding the dynamic plasticity of morphological construction in tea plants.

Different cultivation modes possibly achieve differentiated stage-specific regulation of these plastic traits by altering the source-sink relationship and micro-environment of the tea plants. For instance, the Hilly Tea Monoculture (HT) and Plain Tea-Soybean Intercropping (PTS) modes maintained larger bud width and size throughout the sprouting period (Figures 3B, D). The width advantage in the HT mode might benefit from its relatively higher temperature and moderate radiation (Table 1), conditions considered conducive to promoting cell lateral expansion (Brown and Rickless, 1949; Casal and Balasubramanian, 2019). The advantage of the PTS mode likely stems from the unique biological nitrogen fixation of leguminous crops, providing a sufficient nitrogen nutrition base for the lateral growth of tea buds (Duan et al., 2021; Pokharel et al., 2023). On the other hand, the bud number advantage shown by Plain Tea Monoculture (PT) and Plain Tea-Forest Intercropping (PTF) in the mid-to-late stages (Figure 3C) might be related to the promotion of axillary bud differentiation by higher solar radiation in the PT mode (Table 1 shows its highest solar radiation) (Leduc et al., 2014; Samuoliene et al., 2017).

Previous research generally holds that high-altitude environments, due to higher air humidity and diffuse light, usually favor increased free amino acid content, reduced tea polyphenol levels, and a lower polyphenol-to-amino acid ratio in tea, thereby forming a “refreshing” quality style (Han et al., 2017; Li et al., 2022; Ren et al., 2025). However, this study observed an opposite trend: plain tea gardens (PT/PTS) exhibited typical “refreshing” quality characteristics, while hilly tea gardens (HT/HTF) leaned towards a “mellow and robust” style. In this study, the core driver of chemical quality differentiation lies in the significant difference in free amino acid content, directly reflected in the significant change of the polyphenol-to-amino acid ratio (Figures 4A, C). In contrast, tea polyphenol content remained relatively stable across treatments (Figures 4B, 6A), indicating that under the conditions of this study, the difference in tea chemical quality was primarily dominated by nitrogen metabolism products—especially the content of free amino acids—rather than the carbon metabolism product, tea polyphenols.

This free amino acid-dominated quality differentiation pattern profoundly reflects the differential regulation of tea plant nitrogen metabolism pathways by the micro-environments created by different cultivation modes. In the plain modes (PT/PTS), milder light, higher air humidity, and good soil moisture conditions (Table 1) collectively created a micro-environment favorable for nitrogen assimilation and amino acid accumulation (Jeyaramraja et al., 2003; Kc et al., 2021; Qifang et al., 2025). Among them, the PTS mode, further enhanced by the biological nitrogen fixation of leguminous crops, significantly increased rhizosphere nitrogen availability, strengthening its “refreshing” quality characteristics (Ruan et al., 2007; Duan et al., 2021; Wang et al., 2022). In contrast, amino acid accumulation was generally limited in the hilly modes (HT/HTF), but the limiting mechanisms differed: the lower soil water content (31.46%) in the HT mode might induce water stress, inhibiting the transport of amino acids from roots to new shoots (Good and Zaplachinski, 1994; Jeyaramraja et al., 2003; Qifang et al., 2025). Although the HTF mode had higher soil moisture and lower radiation, its lowest average temperature (16.69°C) was below the optimal growth temperature range for tea plants (20–25°C), significantly inhibiting the efficiency of theanine synthesis in roots and its transport to the apical parts (Wu et al., 2025), reflecting that water and temperature factors differentially dominated the suppression of nitrogen metabolism in different hilly modes.

This study further quantified, through effect sizes, that the regulatory effect of cultivation mode on the final morphology of tea buds monitored at the late sprouting stage (0.753) was greater than its effect on the simultaneously measured chemical quality indicators (0.530). Even the response of morphological growth rates (0.699) to cultivation mode was stronger than that of chemical quality (Figure 6B). This result clearly demonstrates that, on an agronomic timescale, the external morphological traits of tea buds exhibit higher cultivation controllability than their internal chemical quality traits.

To cope with unstable environments, plants can adapt by adjusting their morphological structure or by rapidly altering their metabolite composition (Dong and Lin, 2021; Zhang et al., 2022). However, these two adaptive strategies differ fundamentally in the underlying mechanisms of their plasticity. The production and turnover of secondary metabolites can be very rapid; their biochemical response to and cessation following environmental signals are far more sensitive and reversible than morphological adjustments (Metlen et al., 2009). In contrast, the morphogenesis of leaves or buds involves complex developmental programs such as cell division, expansion, and tissue differentiation. Changes in morphology are often irreversible or accumulate slowly (Fritz et al., 2018). Therefore, although metabolic traits are environmentally sensitive, their strong dynamic fluctuations make it difficult to achieve stable, directional, and cumulative changes through single or short-term agronomic practices. In contrast, once morphological traits undergo directional changes in response to environmental influences, they are more easily fixed and observed, thus exhibiting greater potential for agronomic manipulation.

This study is the first to quantitatively verify this principle within the tea plant system, revealing that the shaping effect of cultivation mode on morphology (particularly width and number) is significant and stable. Although environmental factors also drive changes in key tea metabolites (e.g., tea polyphenols, amino acids) (Wu et al., 2025), their responses are likely more susceptible to interference from multiple factors such as transient climatic fluctuations and developmental stage transitions. This may result in their effect size in response to cultivation mode being lower than that of morphological traits at a given point in time. This understanding not only deepens the comprehension of the hierarchical regulation of “morphology-metabolism” in tea garden ecosystems but also provides a key theoretical basis for prioritizing the directional optimization of tea bud appearance traits through precise microenvironment management (e.g., targeted regulation of light and temperature resources via intercropping or shading). Future research could further integrate continuous time-series dynamic monitoring to analyze the differential response trajectories of morphological and metabolic plasticity over longer cycles, thereby refining the process-based theoretical system for precision cultivation.

Through dynamic monitoring, this study found no significant correlations between all chemical quality indicators (free amino acids, tea polyphenols, and the polyphenol-to-amino acid ratio) and the morphological indicators of tea buds (length, width, size, number, and their growth rates) at the late sprouting stage (Figure 8). This clear “morphology-chemistry” decoupling phenomenon challenges the traditional empirical belief that intrinsic tea quality can be inferred from appearance traits, such as bud size. The underlying mechanism may stem from a fundamental hierarchical separation between the biological processes of morphogenesis and metabolite accumulation, in terms of their regulatory logic, temporal scales, and resource allocation.

From the perspective of molecular regulation, morphological development and chemical quality formation may be controlled by distinct genetic programs and environmental response networks. The morphogenesis of tea buds, especially key traits like size, is primarily governed by a relatively fixed developmental program. Research indicates that key genes such as CsKNOX6 play a central role in regulating tea bud cell division and expansion, and variation in their expression can significantly affect bud size, reflecting the strong genetic constraint on morphological development (Zhang et al., 2025b). More importantly, the morphological plasticity of leaves (buds) itself is a highly integrated, modular process controlled by complex gene regulatory networks (GRNs). Environmental signals (e.g., light, temperature) must influence key components within these networks, such as transcription factors, chromatin states, and hormone signaling pathways, to trigger amplified yet relatively slow morphological adjustments (Gonzalez et al., 2012; Fritz et al., 2018). This regulatory mode determines the “inertia” and cumulative effects of morphological traits in response to the environment.

In stark contrast, the biosynthesis and accumulation of key components determining tea flavor chemical quality—amino acids (e.g., theanine) and tea polyphenols (primarily catechins)—are governed by a highly dynamic and plastic metabolic network. These secondary metabolites are core components of the plant’s chemical defense system against environmental stresses (both biotic and abiotic), and their synthesis is characterized by rapid induction and reversibility (Metlen et al., 2009; Scheres and van der Putten, 2017). Substantial evidence shows that a range of environmental factors, including seasonal shifts, water stress, temperature fluctuations, and light changes, can rapidly and significantly (with variation amplitudes up to 50%) alter the content of secondary metabolites in tea leaves. However, the direction and extent of these effects vary depending on the specific environment, cultivar, and management practices, and there are even contradictory reports, highlighting the extreme complexity and context-dependency of metabolic network responses (Ahmed et al., 2019; Wu et al., 2025). In short, morphological development addresses “how to build a stable structure,” while chemical quality formation addresses “how to perform dynamic biochemical defense and adaptation.” There is an essential difference in their regulatory objectives and response dynamics.

This difference in regulatory hierarchy may lead to a temporal misalignment between the two processes on the developmental timescale. Morphological development (e.g., cell division, tissue differentiation) is a continuous, resource-intensive process, and its changes, once initiated, are not easily reversed. In contrast, the synthesis and turnover of secondary metabolites may fluctuate at a faster pace in response to transient environmental signals. The observations in this study were concentrated in the specific time window of the late sprouting stage, potentially capturing a “phase difference” between the key stage of morphological development and the dynamic equilibrium period of chemical substances. This temporal asynchrony might be an important reason for observing phenotypic decoupling at a single time point. Other studies also hint at the complexity of morphology-metabolism relationships. For instance, in tea leaves, photosynthetic and respiratory parameters were significantly correlated with tea polyphenol content but not with total amino acid content, indicating that the coupling strength between different metabolic pathways and physiological functions inherently differs (Li et al., 2016).

Furthermore, internal resource allocation trade-offs within the plant may provide a further explanation for the observed stage-specific decoupling phenomenon. The lack of correlation between tea bud morphogenesis (growth) and chemical quality formation (defense) can be interpreted through the classic “ theory of plant defense” in plant ecology. This theory posits that under limited resource conditions, plants cannot simultaneously maximize investment in both primary growth (e.g., tissue expansion) and secondary metabolic defense (e.g., synthesis of phenolic compounds) (Coley et al., 1985; Herms and Mattson, 1992; Stamp, 2003). As mentioned above, our study indicates that trade-offs already exist among different morphological components during plant growth by the late sprouting stage (e.g., between bud “width” and “number”) (Figure 7). Therefore, during the rapid sprouting phase, the developmental program likely prioritizes the allocation of resources to core morphogenetic processes, while the allocation for synthesizing key secondary metabolites (e.g., theanine, catechins) is relatively constrained. This differential resource allocation at critical developmental stages can lead to independent variation trajectories between morphological and chemical traits—that is, the observed stage-specific decoupling phenomenon. In summary, this suggests that morphological construction and chemical quality formation may operate as partially independent modules. Consequently, agronomic measures targeting one module may not induce proportional or linear changes in the other.

The stage-specific decoupling between morphology and chemistry implies that yield- and quality-related traits in tea may be regulated independently. However, this study’s sampling of chemical quality only at a single, late developmental stage limits our ability to characterize dynamic relationships or transient coordination between these trait categories across the entire sprouting period. Therefore, future research should integrate time−series multi−omics (transcriptomics, metabolomics) with continuous, precise phenotyping to dynamically track the trajectories of morphological and chemical traits and to identify the key regulatory nodes underlying their independent or coupled expression.

The systematic understanding described above lays an important foundation for developing quality-oriented tea garden management strategies. The results of this study can provide references for integrating multi-level strategies from macro-mode selection to field micro-management. The following preliminary ideas are elaborated to offer insights for the targeted regulation of tea quality.

First, in the strategic selection of cultivation modes, it should be closely aligned with the quality requirements of the target tea category. The results of this study indicate that Plain Tea-Soybean Intercropping (PTS) is the preferred mode for producing “refreshing” premium green tea, as it combines the highest free amino acid content (4.3%) with significantly larger tea bud width (Figures 3B, 4A), providing ideal raw material for shaping high-end green tea with “good taste and beautiful appearance”. Conversely, Hilly Tea Monoculture (HT), due to its higher polyphenol-to-amino acid ratio and maintained good bud width (Figures 3B, 4A), is more suitable for developing “mellow and robust” black tea products. This quality potential-based mode matching is a key decision for maximizing tea garden ecosystem services and economic benefits at the source.

Secondly, during the dynamic process of tea bud sprouting, stage-specific precise morphological regulation should be implemented. Based on the inherent programmability and plasticity windows of tea bud development, management measures need to vary with time. In the early sprouting stage, when tea bud width shows a significant decrease (-21%) (Figure 1B), the management core should focus on “preserving width”, potentially through strategies like foliar application of calcium fertilizer to enhance cell wall stability and delay lateral contraction. Entering the mid-to-late sprouting stage, when the increase in tea bud length significantly accelerates and the growth rate of tea bud number decreases (Figures 1A, C), the focus should shift to “promoting length and stabilizing density”, potentially by ensuring timely nitrogen supply to promote longitudinal elongation.

Finally, in response to the stage-specific “morphology-chemistry” decoupling phenomenon, a new paradigm of synergistic management must be developed. We propose establishing a “dual-track monitoring” system to achieve parallel optimization of yield and quality. Track one: use image analysis technology to track key morphological indicators (e.g., width/number ratio) in real-time (Zhang et al., 2019; Jiang et al., 2025a; Sun et al., 2025). When the absolute value of their correlation (|r|) exceeds the competition threshold of 0.5, guide corresponding “width-preserving” or “density-increasing” agronomic operations promptly. Track two, which is key to breaking the decoupling bottleneck, is to actively explore the use of multispectral or hyperspectral remote sensing technology to directly and non-destructively monitor the chemical components of young shoots (e.g., amino acid accumulation dynamics) (Ren et al., 2024; Jiang et al., 2025b). This would bypass the traditional misconception of indirectly inferring quality from morphology, ultimately enabling direct and precise regulation of tea chemical quality.