Medicinal Plant Research 2026, Vol.16, No.2 http://hortherbpublisher.com/index.php/mpr © 2026 HortHerb Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved.
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Medicinal Plant Research (online), 2026, Vol. 16, No.2 ISSN 1927-6508 http://hortherbpublisher.com/index.php/mpr © 2026 HortHerb Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Latest Content Analysis of the Mechanisms by Which Shading Environment Affects the Growth and Medicinal Quality Formation of Tetrastigma hemsleyanum Jianhui Li Medicinal Plant Research, 2026, Vol. 16, No. 2, 92-109 Technical Pathways for Tissue Culture Rapid Propagation and Improvement of Transplant Survival Rate inDendrobium officinale Xinchao Cao Medicinal Plant Research, 2026, Vol. 16, No. 2, 110-125 Construction of a Technical System for Rhizome Propagation and High-Quality Seedling Production of Polygonatum sibiricum JiakaiMa Medicinal Plant Research, 2026, Vol. 16, No. 2, 126-140 Conservation of Rare Medicinal Plant Resources and Artificial Replacement Cultivation Pathways of Anoectochilus roxburghii WeiduoLiu Medicinal Plant Research, 2026, Vol. 16, No. 2, 141-153 Evaluation of the Effects of Harvest Period and Drying Methods on the Quality of Hangbaiju Weiying Gao Medicinal Plant Research, 2026, Vol. 16, No. 2, 154-168
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 92 Research Insight Open Access Analysis of the Mechanisms by Which Shading Environment Affects the Growth and Medicinal Quality Formation of Tetrastigma hemsleyanum Jianhui Li Jiande Shouchang Forest Farm of Zhejiang, Jiande, 311600, Zhejiang, China Corresponding email: 354093255@qq.com Medicinal Plant Research, 2026, Vol.16, No.2 doi: 10.5376/mpr.2026.16.0006 Received: 20 Feb., 2026 Accepted: 24 Mar., 2026 Published: 05 Apr., 2026 Copyright © 2026 Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li J.H., 2026, Analysis of the mechanisms by which shading environment affects the growth and medicinal quality formation of Tetrastigma hemsleyanum, Medicinal Plant Research, 16(2): 92-109 (doi: 10.5376/mpr.2026.16.0006) Abstract This study explores the mechanisms by which shading environments affect the growth and medicinal quality formation of Tetrastigma hemsleyanum. T. hemsleyanumis an important medicinal vine in China, and its tuberous roots and aerial parts are rich in bioactive compounds, including flavonoids, polysaccharides, and phenolic acids, which have medicinal development value due to their anti-inflammatory, antioxidant, immunomodulatory, and antitumor activities. With the decline of wild resources and the increasing demand for artificial cultivation, achieving high-yield and high-quality production of T. hemsleyanum through light environment regulation has become a key issue in its standardized cultivation and industrial development. This study analyzes the ecological habits and low-light adaptation basis of T. hemsleyanum, elucidates the effects of shading on morphogenesis, biomass accumulation, photosynthetic pigments, photosynthetic efficiency, antioxidant systems, carbon-nitrogen metabolic balance, and the accumulation of flavonoids, polysaccharides, and phenolic compounds, and further discusses the roles of light signal perception, signal transduction pathways such as COP1-HY5, key enzyme genes, and transcription factor regulation in medicinal quality formation. Existing studies indicate that T. hemsleyanum exhibits obvious shade-adaptive characteristics, and approximately 67%~70% shading is generally beneficial for maintaining relatively high net photosynthetic rate, stomatal conductance, and leaf function, while also promoting vine growth, leaf expansion, and tuberous root development. In contrast, strong light or excessive shading may inhibit photosynthetic efficiency and disrupt carbon assimilation and biomass allocation. In the future, shading intensity, light quality regulation, cultivation model optimization, and multi-index quality evaluation systems should be integrated to establish standardized shading cultivation techniques suitable for different ecological regions and growth stages of T. hemsleyanum, thereby providing a theoretical basis for resource conservation, high-quality medicinal material production, and industrial utilization. Keywords Tetrastigma hemsleyanum; shading environment; photosynthetic physiology; secondary metabolism; medicinal quality 1 Introduction Tetrastigma hemsleyanumis a high-value Chinese medicinal vine, and both its roots and aerial parts are widely used. With increasing market demand and intensified overharvesting, the utilization of T. hemsleyanumresources is rapidly shifting from wild collection to artificial cultivation (Hu et al., 2021). Its medicinal quality largely depends on light-sensitive secondary metabolites; therefore, shading management has become a key issue in standardized and high-quality production (Zhang et al., 2021). Traditionally, T. hemsleyanum has been used to treat fever, pneumonia, asthma, hepatitis, rheumatism, and other inflammatory and infectious diseases, and it is known in folk practice as a “natural plant antibiotic” (Ji et al., 2020). Modern studies have identified more than 140 compounds in this species, among which flavonoids and polysaccharides are representative active components, exhibiting antitumor, anti-inflammatory, antioxidant, immunomodulatory, and antipyretic activities. Total flavonoids from the roots of T. hemsleyanum can inhibit colorectal tumor growth and regulate gut microbiota (Han et al., 2023), while polysaccharides from the roots and aerial parts show significant antitumor, antipyretic, and immunomodulatory effects in vivo. These findings indicate that T. hemsleyanum is a potential resource for developing novel antitumor and immunomodulatory products and also provide strong impetus for its industrial development. For medicinal plants, light environment regulation is a core agronomic measure that simultaneously affects biomass and secondary metabolite accumulation (Zhang et al., 2021). In many medicinal plants, shading or light
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 93 intensity regulation has been shown to alter photosynthesis, pigment content, and the levels of phenolics, flavonoids, and other bioactive compounds. The optimal state often occurs under moderate shading rather than full sunlight or deep shading (Xu et al., 2020; Gao et al., 2025). In shade-tolerant or understory herbaceous medicinal plants, appropriate shading can simultaneously increase aboveground yield and enhance the accumulation of specific medicinal metabolites, thereby improving overall medicinal value. However, plant responses to the light environment are highly species-specific and are jointly affected by light intensity, spectral quality, and duration. Therefore, it is difficult to directly apply a universal “light formula” to all medicinal crops. This study explores the mechanisms by which shading environments affect the growth and medicinal quality formation of T. hemsleyanum. Existing studies on the physiological characteristics of T. hemsleyanumhave only briefly addressed light effects, and there remains a clear knowledge gap regarding how the light environment shapes its growth process and medicinal quality formation. Given the increasing scarcity of wild resources and the rapid expansion of cultivated areas, it is necessary to clarify the mechanisms by which shading environments regulate the growth of T. hemsleyanum and the accumulation of key active components. On the one hand, standardized light and shading management is important for improving biomass, stabilizing quality markers such as flavonoids and polysaccharides, supporting quality control, and promoting industrial upgrading. On the other hand, clarifying how light intensity and shading affect photosynthesis, antioxidant defense, and secondary metabolism in this species will enrich the theoretical basis for precise light environment regulation in medicinal plants. This study focuses on analyzing the mechanisms by which shading environments influence the growth and medicinal quality formation of T. hemsleyanum, aiming to provide scientific reference for its standardized cultivation, quality evaluation, and sustainable industrial development. 2 Ecological Habits and Shading Adaptation Basis of Tetrastigma hemsleyanum 2.1 Natural habitat and low-light adaptation characteristics of Tetrastigma hemsleyanum Tetrastigma hemsleyanum is a perennial herbaceous climbing vine belonging to the genus Tetrastigma in the family Vitaceae, and it is one of the important medicinal plant resources in China. Its natural distribution is mainly concentrated in warm evergreen forests in subtropical and tropical regions of China. It is commonly found in understory habitats, forest edges, valleys, streamside areas, and hillside shrublands at altitudes of 300-1300 m, and may also extend to regions such as Hainan and Taiwan (Ren et al., 2025). From an ecological perspective, T. hemsleyanumprefers cool and humid environments, relatively high air humidity, loose soils rich in humus, and yellow or yellow-brown soils. Its natural habitats are generally characterized by sufficient scattered light, weak direct sunlight, and relatively stable hydrothermal conditions (Ji et al., 2020; Hu et al., 2021). This indicates that T. hemsleyanum is not a typical heliophilous plant, but is more suitable for growth in semi-shaded and humid environments with a certain degree of canopy cover. This also provides an ecological basis for its application in understory cultivation, trellis cultivation, and intercropping systems. During long-term adaptation to understory or semi-shaded environments, T. hemsleyanumhas developed a series of low-light adaptation characteristics. The plant mainly grows as a climbing vine and can extend outward by relying on surrounding vegetation or supports, thereby obtaining suitable scattered light resources. As the main photosynthetic organs, leaves are highly sensitive to changes in light conditions. Under low-light conditions, they can improve light interception capacity by regulating leaf area, chlorophyll content, and spatial leaf distribution. Ensemble habitat modeling further indicates that the current highly suitable habitats of T. hemsleyanumaremainly concentrated in subtropical regions jointly constrained by specific temperature and precipitation conditions, showing strong climatic adaptation specificity. Genomic and landscape genomic studies also show that T. hemsleyanumexhibits obvious local adaptation to heterogeneous climates. Winter precipitation and other climatic factors can explain a considerable proportion of its genomic variation, and many adaptive loci are associated with stress responses and environmental adaptation (Ren et al., 2025). Although direct measurements of the natural canopy light environment of T. hemsleyanumremain limited, its distribution in evergreen forests, preference for cool and humid environments, and the need to avoid strong light in bionic cultivation collectively support the view that it has a shade-adapted, low-light ecological strategy (Xu et al., 2018; Hu et al., 2021).
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 94 2.2 Fundamental role of light intensity in the growth and development of Tetrastigma hemsleyanum Light is one of the most important ecological factors in the growth and development of T. hemsleyanum. It not only provides energy for photosynthesis, but also acts as an environmental signal involved in regulating plant morphogenesis, substance accumulation, and metabolic activities. Suitable light intensity is beneficial for improving leaf photosynthetic efficiency, promoting organic matter synthesis and transport, and providing a material basis for vine elongation, leaf expansion, and tuberous root enlargement. Shading experiments have shown that light intensity is a key factor regulating the growth, photosynthesis, and pigment accumulation of T. hemsleyanum. Under different shading levels, leaf size and net photosynthetic rate (Pn) reach relatively high levels under approximately 67%~70% shading, whereas stronger light and excessive shading both reduce plant growth and carbon assimilation capacity (Dai et al., 2009; Xu et al., 2018). This suggests that T. hemsleyanumhas a clear suitable range of light intensity, and that either excessively strong or insufficient light is unfavorable for its sustained growth and formation of medicinal organs. Both excessively high and excessively low light intensity may adversely affect T. hemsleyanum. Under strong light conditions, leaf transpiration increases and plant water consumption accelerates. When accompanied by high temperature and insufficient soil moisture, this may easily lead to leaf wilting, scorching, or photoinhibition, thereby reducing photosystem stability and photosynthetic efficiency. Studies have shown that under full sunlight and low-shading conditions, electron transport rate and photochemical quenching in T. hemsleyanumare inhibited, while non-photochemical quenching increases, indicating that excessively strong light can induce photoinhibition and reduce light-use efficiency. Conversely, under long-term excessive shading or insufficient low-light conditions, although T. hemsleyanum can enhance low-light capture capacity by increasing chlorophyll a, chlorophyll b, and total chlorophyll contents and reducing the chlorophyll a/b ratio, the accumulation of net photosynthetic products remains limited due to insufficient photosynthetically active radiation (Dai et al., 2009). Light response curve studies also indicate that the net photosynthetic rate of T. hemsleyanum increases rapidly under moderate photon flux density, then tends to become saturated, and decreases under high-light conditions, while the suitable light saturation point and maximum net photosynthetic rate mainly occur under moderate shading conditions (Xu et al., 2018). Therefore, the effect of light intensity on T. hemsleyanumis clearly dual in nature, and the key lies in maintaining a dynamic balance among light energy utilization, carbon assimilation, and stress alleviation. 2.3 Significance of shading environment for adaptation to artificial cultivation The shading environment has important ecological regulatory significance in the artificial cultivation of T. hemsleyanum. Since the natural habitat of T. hemsleyanumis mostly semi-shaded and humid, exposing artificially cultivated plants completely to strong light may easily create a mismatch between their ecological niche requirements and the cultivation environment. In recent years, with the decline of wild T. hemsleyanumresources and increasing demand for medicinal materials, artificial cultivation has expanded rapidly, making light environment management a core issue for sustainable production. Based on the fact that T. hemsleyanumnaturally grows in forest environments and is sensitive to strong light, bionic cultivation has been considered an important approach to meeting medicinal material demand and improving cultivation adaptability (Xu et al., 2018). By using shading nets, trellises, understory intercropping, or intercropping with tall-stemmed crops, direct light intensity can be reduced, the proportion of scattered light can be increased, and the field microclimate can be improved, thereby creating a growth environment close to its natural habitat. Relevant studies suggest that shading measures capable of achieving approximately 67%~70% shading may be adopted in cultivation, because higher light intensity inhibits its photosynthetic activity and growth, while excessive shading restricts carbon assimilation (Dai et al., 2009). From the perspective of production practice, the value of shading treatment lies not only in promoting the growth of T. hemsleyanum, but also in regulating the relationship between yield and quality. Under suitable shading conditions, T. hemsleyanumcan affect the formation and accumulation of active components such as flavonoids, polysaccharides, and phenolic compounds by improving leaf photosynthetic function, maintaining antioxidant system activity, regulating carbon-nitrogen metabolism, and promoting secondary metabolic processes. Studies on
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 95 other shade-tolerant medicinal plants also support this pattern, indicating that moderate shading can improve growth, photosynthetic performance, and secondary metabolite accumulation, whereas full sunlight and deep shading may both have adverse effects. For example, in medicinal plants such as Eleutherococcus senticosus, Pinellia ternata, Paris polyphylla var. chinensis, and Polygala fallax, moderate shading can increase chlorophyll content, optimize photosystem function, and increase biomass or certain active components, whereas excessively strong or weak light may lead to growth inhibition, light damage, or reduced accumulation of active components (Xu et al., 2020; Liang et al., 2022; Gao et al., 2025; Liu et al., 2026). Reviews on light-regulated secondary metabolism further indicate that precise control of light intensity and light quality is an important means of enriching valuable medicinal metabolites, which also highlights the importance of shading regimes in quality-oriented cultivation of T. hemsleyanum(Zhang et al., 2021). Therefore, establishing a rational shading management model not only helps improve the adaptability of T. hemsleyanumto artificial cultivation environments, but also provides important technical support for high-quality, efficient, and standardized cultivation. Especially in medicinal plant cultivation, yield improvement does not necessarily equate to quality enhancement. How to achieve coordination among tuberous root yield, active component content, and commercial traits of medicinal materials is a core issue in optimizing T. hemsleyanum cultivation technology. In the future, shading cultivation of T. hemsleyanum should be based on a clear understanding of its ecological habits and photosynthetic adaptation mechanisms, and should further integrate shading intensity, light quality regulation, cultivation models, and quality evaluation indicators to establish a widely applicable standardized light environment management scheme, thereby supporting resource conservation, stable medicinal material quality, and industrial development of T. hemsleyanum. 3 Effects of Shading Environment on Morphogenesis and Biomass Accumulation of Tetrastigma hemsleyanum 3.1 Effects on plant height, vine growth, and branching The shading environment first affects the aboveground morphogenesis of Tetrastigma hemsleyanum, especially in terms of plant height, vine elongation, and branch growth. As a perennial vine, T. hemsleyanumoften grows in understory or semi-shaded and humid environments in the wild, where it receives scattered light filtered through the forest canopy. Therefore, its artificial cultivation also requires light regulation to approximate its natural ecological niche requirements as closely as possible (Ji et al., 2020). Vine growth capacity is directly related to spatial expansion, leaf distribution, and light resource acquisition in T. hemsleyanum. Under moderate shading conditions, plants can enhance their utilization of scattered light by increasing vine length, adjusting internode distance, and improving the spatial arrangement of leaves. This morphological change represents an adaptive response to low-light environments, which helps expand the photosynthetic area and improve the light interception efficiency of the plant canopy under limited light resources. The effects of shading on vine growth in T. hemsleyanum vary significantly with shading intensity. Shading experiments have shown that under full sunlight or only 50% shading, photosynthetic electron transport and photochemical quenching in T. hemsleyanumare inhibited, while photosynthetic activity and plant growth decline, indicating that strong light conditions suppress overall plant growth. In contrast, when light is reduced to approximately 67%~70% shading, the net photosynthetic rate, light saturation point, and maximum photosynthetic rate are higher than those under weaker shading treatments, indicating that this shading level is more conducive to carbon assimilation and vegetative vine growth (Xu et al., 2018). However, if shading is excessive, such as reaching 75%-90% or higher, insufficient photosynthetically active radiation restricts carbon assimilation and slows growth (Dai et al., 2009). Therefore, plant height, vine elongation, and branch formation in T. hemsleyanum are jointly constrained by photoinhibition under strong light and insufficient carbon supply under deep shading, while moderate to relatively high shading is more favorable for vine extension and coordinated plant structure formation. From the general perspective of plant responses to shading, reduced light or a decreased red/far-red ratio can induce shade-avoidance responses, manifested as stem and internode elongation, but often at the cost of reduced
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 96 branching and limited development of harvestable organs (Yang and Li, 2017). Similar phenomena have also been observed in leguminous plants, where shading can promote taller and thinner plants while reducing the number of lateral branches and aboveground biomass. For naturally shade-tolerant T. hemsleyanum, moderate shading is more likely to result in adaptive elongation and canopy optimization rather than simple etiolation. However, under excessive shading, excessive vine elongation, overly extended internodes, weak stems, and suppressed lateral branching may still occur, ultimately affecting leaf area formation and photosynthetic product accumulation. Therefore, in cultivation, “vine elongation” should not be simply equated with “good growth”; instead, branch number, leaf distribution, vine robustness, and underground tuberous root development should be comprehensively evaluated. 3.2 Effects on leaf morphology and leaf area expansion Leaves are the main organs through which T. hemsleyanumperforms photosynthesis and senses changes in the light environment. Therefore, changes in leaf morphology under shading conditions are important manifestations of its low-light adaptation. Leaf traits of T. hemsleyanumare sensitive to shading environments and reflect typical shade-leaf characteristics. As shading increases, chlorophyll a, chlorophyll b, and total chlorophyll contents increase, while the chlorophyll a/b ratio decreases, indicating adaptive adjustment of the light-harvesting antenna system to capture limited photons more efficiently under low-light conditions (Dai et al., 2009; Xu et al., 2018). In general, under moderately low-light environments, T. hemsleyanum can enhance light capture capacity by expanding individual leaf area, increasing total leaf area, and increasing photosynthetic pigment content. Studies have shown that leaves of T. hemsleyanumreach their largest size under approximately 67% shading, whereas full sunlight, 50% shading, and deep shading of approximately 90% all result in smaller leaves (Dai et al., 2009). Leaf area expansion can increase the plant’s absorption range of scattered light, helping compensate for the decrease in light intensity per unit leaf area. These changes are consistent with general patterns observed in shade-tolerant medicinal plants and forest plants, in which moderate shading, compared with no shading or excessive shading, is more conducive to increasing leaf area, improving seedling quality, and enhancing leaf function (Xue et al., 2023; Liu et al., 2026). In other shade-tolerant medicinal plants, low to moderate shading can thin the palisade tissue, increase total leaf thickness, and improve mesophyll structure, thereby promoting light absorption and carbon dioxide diffusion (Li et al., 2025). In T. hemsleyanum, increased chlorophyll content under approximately 67%~70% shading, together with improved net photosynthetic rate and other photosynthetic parameters, suggests that its leaf structure and function may also undergo optimization favorable for low-light utilization (Dai et al., 2009; Xu et al., 2018). However, leaf area expansion does not necessarily indicate increased biomass accumulation. If shading intensity is too high, leaves may show certain shade-adaptive characteristics, such as deeper green color, increased chlorophyll content, or thinner leaf blades. Nevertheless, due to insufficient photosynthetically active radiation, net photosynthetic capacity per unit leaf area may decline, causing leaves to shift from highly efficient production organs to organs with relatively high maintenance costs. Long-term deep shading may also reduce leaf structural stability and stress resistance and increase the risk of disease occurrence. When shading is excessive, the decline in light saturation point and photosynthetic capacity in T. hemsleyanum limits carbon acquisition, thereby restricting leaf expansion and total leaf area formation (Xu et al., 2018). Therefore, the effects of shading on leaf morphology should be evaluated comprehensively from three aspects: leaf area expansion, leaf functional maintenance, and photosynthetic efficiency improvement. Among these, moderate shading regimes are more conducive to allowing T. hemsleyanumto fully express shade-leaf morphological potential, improve canopy light interception, and promote biomass accumulation. 3.3 Effects on tuberous root enlargement and biomass allocation The main medicinal organs of T. hemsleyanumare enlarged spindle-shaped tuberous roots. These tuberous roots serve both as storage tissues and as pharmacologically active tissues, and their enlargement and dry matter accumulation are directly related to medicinal yield and commercial value (Figure 1) (Ji et al., 2020). The effect of shading environment on tuberous root formation essentially depends on the coordination between aboveground
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 97 photosynthetic product supply and underground assimilate allocation. At present, direct studies on the relationship between shading and tuberous root enlargement in T. hemsleyanum remain limited, and existing research has mainly focused on changes in aboveground photosynthesis under different light intensities (Hu et al., 2021). Current data indicate that unsuitable light environments, such as strong light, high temperature, and low humidity, reduce photosynthetic activity and slow plant growth in T. hemsleyanum, thereby indirectly limiting carbohydrate supply to the roots (Xu et al., 2018). In contrast, 67%~70% shading can maintain relatively high maximum net photosynthetic rate and quantum efficiency, creating favorable conditions for sustained assimilate production and its storage in tuberous roots (Dai et al., 2009). Figure 1 The aerial part (A), root tuber (B) and raw herb (C) of T. hemsleyanum Studies on other medicinal plants with storage organs help explain the possible biomass allocation patterns of T. hemsleyanumunder different shading regimes. In shade-responsive species, moderate shading generally increases total biomass more effectively than full sunlight or deep shading, and may also increase root or storage organ biomass (Liang et al., 2022; Xue et al., 2023). Comprehensive studies of biomass allocation have shown that plants under environmental stress or resource limitation often allocate a relatively greater proportion of biomass to underground parts, thereby increasing the root-shoot ratio. However, this does not necessarily mean improved medicinal yield, because increased underground allocation may be accompanied by damage to aboveground photosynthetic structures and a decline in total biomass (Qi et al., 2019). In medicinal herbaceous plants, light shading may reduce the root-shoot ratio while increasing leaf biomass and total yield; in contrast, high light and dense planting may promote biomass allocation to roots, but at the expense of restricted aboveground growth (Ahmed et al., 2024). In storage tuber crops such as potato, simulated shading promotes stem elongation but reduces tuber yield, indicating that excessive shading may redirect assimilates from storage organs toward stem elongation (Gómez-Ocampo et al., 2023). Therefore, from the perspective of medicinal material production, an ideal shading environment should not simply promote stem and leaf growth, nor should it simply increase the root-shoot ratio. Instead, it should maintain a dynamic balance between aboveground photosynthetic structure formation and underground medicinal organ accumulation. T. hemsleyanumlikely has an optimal shading range close to the 67%~70% shading level identified in photosynthetic performance studies. Within this range, aboveground assimilation and underground storage processes can be well coordinated, thereby simultaneously supporting vigorous vine growth and effective tuberous root enlargement. In contrast, both strong light stress and excessively deep shading may lead to unfavorable biomass allocation and reduced medicinal yield. Therefore, in T. hemsleyanum cultivation, shading intensity should be reasonably controlled according to different growth stages so as to maintain good vegetative growth while ensuring tuberous root formation and medicinal yield improvement.
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 98 4 Effects of Shading Environment on Photosynthetic Physiology and Stress Resistance of Tetrastigma hemsleyanum 4.1 Effects on photosynthetic pigments and light-harvesting capacity Photosynthetic pigments are an important material basis for light energy absorption, transfer, and conversion in Tetrastigma hemsleyanum, and changes in their content and composition directly reflect the plant’s adaptability to shading environments. Shading treatment can significantly alter the pigment system of T. hemsleyanum and related shade-tolerant plants, thereby reshaping their light-harvesting capacity. Studies have shown that, in T. hemsleyanum, chlorophyll a, chlorophyll b, and total chlorophyll contents gradually increase with increasing shading intensity, while the chlorophyll a/b ratio decreases, indicating a typical shade-leaf adaptive expansion of the light-harvesting complex. This adjustment helps enhance the absorption of scattered and weak light under low-light conditions (Dai et al., 2009; Xu et al., 2018). In particular, the increase in chlorophyll b content is important for expanding the light-harvesting antenna system and improving light energy utilization efficiency under weak light. Similar phenomena have also been observed in other shade-managed crops, in which shading promotes the accumulation of chlorophyll and carotenoids and, compared with full sunlight, helps maintain greener leaves and a higher net photosynthetic rate (Elango et al., 2023). In addition to chlorophylls, auxiliary pigments such as carotenoids also participate in light absorption, energy transfer, and photoprotection. Under suitable shading conditions, increases in chlorophyll and carotenoid contents can enhance light absorption capacity and improve the processing efficiency of absorbed light energy. At the same time, they reduce strong light-induced photooxidative pressure and decrease damage caused by excessive light energy accumulation in leaves. Shade-grown leaves usually show a reduced chlorophyll a/b ratio along with structural adjustments, which helps improve the utilization of transmitted light and avoid photoinhibition (Sagun et al., 2022). In overwintering tea plants and other shade-managed crops, shading can also upregulate genes related to chlorophyll and carotenoid metabolism as well as core photosystem protein genes, thereby enhancing light-harvesting capacity under low-light conditions (Simkin et al., 2022; Han et al., 2023). Therefore, moderate shading can enhance the adaptability of T. hemsleyanum to weak-light environments by optimizing pigment composition and the light-harvesting system. However, if shading is excessive, although leaves may exhibit apparent features such as deeper green color and increased chlorophyll content, insufficient incident light energy will still restrict light reactions and carbon assimilation, ultimately reducing photosynthetic production capacity. 4.2 Effects on photosynthetic efficiency and stomatal regulation Photosynthetic efficiency is an important indicator for evaluating the growth potential of T. hemsleyanumunder different light environments. Moderate shading can alleviate physiological stress caused by strong light, high temperature, and excessive water transpiration, helping maintain favorable stomatal opening and photosynthetic system activity. Across a series of shading treatments, the net photosynthetic rate, stomatal conductance, transpiration rate, light saturation point, and maximum net photosynthetic rate of T. hemsleyanumall increased with enhanced shading and reached relatively high levels under approximately 70% shading, before declining under deeper shading. Across different growth stages, the 70% shading treatment consistently showed superior photosynthetic characteristics (Xu et al., 2018). Another shading experiment also showed that under 67% shading, T. hemsleyanum had the largest leaves, the highest net photosynthetic rate, and a light saturation point of 600 μmol·m⁻²·s⁻¹, whereas stronger light and excessive shading both reduced carbon assimilation capacity and plant growth (Dai et al., 2009). These findings indicate that the photosynthesis of T. hemsleyanumexhibits an obvious “moderate optimum” response to shading intensity. Shading also reshapes stomatal regulation and photochemical processes in T. hemsleyanum. Under suitable shading conditions, stomatal conductance and transpiration rate remain relatively coordinated, which helps ensure carbon dioxide entry into leaves for carbon assimilation. Meanwhile, the milder microclimate under shading can reduce leaf water deficit and decrease photosynthetic limitation caused by stomatal closure. Studies have shown that stomatal conductance and transpiration rate in T. hemsleyanum increase as shading rises to 70%, and then decline; unsuitable conditions such as strong light and high temperature reduce photosynthetic activity and slow plant growth (Xu et al., 2018). Under full sunlight and low-shading conditions, electron transport rate and
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 99 photochemical quenching in T. hemsleyanumdecrease, while non-photochemical quenching increases, indicating the occurrence of photoinhibition. Moderate shading, by contrast, can maintain relatively high photochemical efficiency (Dai et al., 2009). Similar patterns have also been reported in other woody and medicinal plants: net photosynthetic rate is relatively high under moderate shading, the functions of photosystem II and photosystem I are more coordinated, whereas strong light or heavy shading may cause photosystem functional imbalance (Barazetti et al., 2021). However, the effect of shading on photosynthetic efficiency is dual in nature. When shading is too strong, insufficient photosynthetically active radiation becomes the main factor limiting photosynthesis in T. hemsleyanum. Under such conditions, even if stomatal conductance does not decline significantly, insufficient light energy received by leaves will restrict both light and dark reactions, resulting in a decrease in net photosynthetic rate. Long-term heavy shading reduces organic matter synthesis, disrupts the balance between respiratory consumption and material accumulation, and further affects robust vine growth, leaf functional maintenance, and underground tuberous root enlargement. Therefore, the key to shading cultivation is not simply to reduce light exposure, but to regulate light intensity rationally so that T. hemsleyanumcan avoid strong light stress while obtaining sufficient light energy to support biomass accumulation and medicinal quality formation. 4.3 Effects on the antioxidant system and cellular homeostasis The shading environment also regulates stress resistance and cellular homeostasis in T. hemsleyanumby affecting the production and scavenging of reactive oxygen species. Regulation of the antioxidant system is an important mechanism by which plants cope with light stress. Although direct studies on antioxidant enzyme activities in T. hemsleyanum remain relatively limited, related studies in model shade-tolerant plants and medicinal plants are more abundant. Under strong light, high temperature, water stress, or other unfavorable light environments, the photosynthetic electron transport chain in leaves is prone to over-reduction, resulting in the accumulation of reactive oxygen species (ROS), which can further induce membrane lipid peroxidation, protein damage, and destruction of photosynthetic structures (García-Caparrós et al., 2020; Mishra et al., 2023). Therefore, plants must rely on enzymatic and non-enzymatic antioxidant systems to remove excess ROS, protect cellular structures, and maintain metabolic stability. The main enzymatic antioxidant components include superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR). These enzymes act cooperatively to convert reactive oxygen species such as superoxide anions and hydrogen peroxide into less harmful products. Meanwhile, non-enzymatic antioxidants such as ascorbic acid, glutathione, carotenoids, and flavonoids can also provide additional redox buffering capacity (García-Caparrós et al., 2020; Rajput et al., 2021). Moderate shading can reduce excessive light energy input, alleviate photooxidative pressure, and help maintain coordinated operation of antioxidant enzyme systems, thereby improving the plant’s buffering capacity against environmental fluctuations. Under different light conditions, many plants can maintain ROS homeostasis by upregulating antioxidant-related gene expression and increasing antioxidant enzyme activities. In the shade-tolerant plant Solidago canadensis, increased shading can induce high expression of SOD, POD, CAT, APX, and GPX genes, thereby enhancing ROS scavenging capacity under shading stress. In shade-tolerant Panax notoginseng, strong light stress increases SOD, POD, and CAT activities, while non-photochemical quenching dissipates excess energy to prevent photooxidative damage (Cun et al., 2023). Jasmine shows rapid changes in SOD, POD, APX, and CAT activities under different shading levels, and these changes are affected by both shading intensity and duration. Moderate shading generally supports more efficient antioxidant responses and reduces membrane lipid peroxidation compared with full sunlight or heavy shading (Deng et al., 2018). Based on these findings, it can be inferred that, in T. hemsleyanum, suitable shading environments may reduce excessive ROS production caused by strong light or extreme shading, support balanced antioxidant enzyme activity, and maintain membrane integrity, osmotic regulation capacity, and
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 100 redox homeostasis, thereby providing a physiological basis for enhanced stress resistance and stable medicinal quality formation. 5 Effects of Shading Environment on Substance Metabolism and Active Component Accumulation inTetrastigma hemsleyanum 5.1 Effects on carbohydrate accumulation and transport Carbohydrates are an important material basis for the growth, development, and medicinal organ formation of Tetrastigma hemsleyanum. Their accumulation level is directly affected by photosynthetic intensity, sugar metabolic activity, and the transport efficiency of assimilates. By altering the light intensity received by leaves, the shading environment further affects the synthesis, allocation, and transport of carbohydrates such as soluble sugars, sucrose, and starch. Studies on light-regulated sugar metabolism indicate that light intensity and light quality can influence starch granule formation, sucrose synthesis, and vascular transport, thereby determining the amount of carbon sources available for plant growth, storage organ development, and secondary metabolism. Under moderate shading conditions, leaves of T. hemsleyanum are expected to maintain relatively stable photosynthetic activity while reducing physiological consumption caused by strong light and high temperature, which is conducive to the continuous formation and effective transport of photosynthetic products. At this stage, leaves function as “source” organs and can provide sufficient carbon support for vine growth and underground tuberous root enlargement. Carbohydrate accumulation is highly sensitive to shading intensity. If shading is excessive, insufficient photosynthetically active radiation restricts carbon assimilation, reducing the production of photosynthetic products in leaves and subsequently affecting sucrose transport to underground tuberous roots and the accumulation of storage substances. In medicinal underground bud plants such as Bletilla striata and Bletilla ochracea, moderate shading or medium light intensity can increase aboveground and tuber dry weight, net photosynthetic rate, and total polysaccharide content, whereas excessive shading leads to a significant decline in these indicators (Xu et al., 2024). Suitable light intensity can promote sucrose production in leaves and improve its transport efficiency to storage organs. In storage organs, sucrose is further converted into key intermediates such as sucrose-6-phosphate, fructose-6-phosphate, glucose-6-phosphate, GDP-mannose, and UDP-glucose, which subsequently participate in polysaccharide biosynthesis (Zhu et al., 2024; Zhu et al., 2025). Conversely, under low-light or long-term shading conditions, glycolysis, galactose metabolism, the pentose phosphate pathway, and the tricarboxylic acid cycle are inhibited in many plants, resulting in reduced sugar reserves and causing plants to shift toward consuming stored carbohydrates (Liu et al., 2020; Shao et al., 2022). Therefore, the regulation of carbon metabolism by shading in T. hemsleyanumis not simply promotive or inhibitory; rather, it depends on whether shading intensity can maintain a balance among photosynthesis, respiratory consumption, and assimilate transport. 5.2 Effects on nitrogen metabolism and carbon-nitrogen balance Nitrogen metabolism is an important basis for vegetative growth and physiological function maintenance in T. hemsleyanum, and it is closely associated with chlorophyll synthesis, protein formation, enzyme activity regulation, and secondary metabolism. Under shading conditions, T. hemsleyanum often needs to adjust leaf structure and photosynthetic pigment composition to adapt to weak-light environments, while chlorophyll, Rubisco, and other photosynthesis-related proteins all require nitrogen for their formation. General studies on carbon-nitrogen regulation have shown that increasing nitrogen allocation in leaves can enhance chlorophyll and Rubisco contents, photosynthetic nitrogen-use efficiency, and carbon assimilation capacity, and can help improve plant growth and carbon storage even under nitrogen-limited conditions (Perchlik and Tegeder, 2018). Therefore, under moderate shading conditions, T. hemsleyanum may enhance light absorption and utilization under weak light by optimizing nitrogen allocation for leaf functional maintenance and photosynthetic system construction, thereby providing a metabolic basis for subsequent substance synthesis and medicinal component accumulation. Shading can also reshape nitrogen metabolism and carbon-nitrogen (C-N) balance, both of which jointly determine photosynthetic capacity, vegetative growth, and secondary metabolite biosynthesis in plants. In tea
Medicinal Plant Research 2026, Vol.16, No.2, 92-109 http://hortherbpublisher.com/index.php/mpr 101 plants, short-term shading can promote leaf nitrogen metabolism and increase amino acid accumulation, whereas long-term or high-intensity shading inhibits sugar metabolism and alters flavonoid metabolic pathways (Li et al., 2020). Under shading conditions, protein hydrolysis and nitrogen redistribution can increase free amino acid content, while catechin and other phenolic compound levels decline, reflecting a shift in carbon-nitrogen allocation direction (Shao et al., 2022). Shading experiments in forest plants have shown that, as shading increases, the leaf C:N ratio decreases while the N:P ratio increases, and non-structural carbohydrates are closely associated with C: N: P stoichiometric characteristics, suggesting a dynamic trade-off between carbon storage and nutrient utilization under low-light environments (Liu et al., 2020). For T. hemsleyanum, if shading is appropriate, carbon supply and nitrogen utilization can remain relatively coordinated, which is beneficial for protein synthesis, enzymatic reactions, and normal operation of metabolic pathways. If shading is excessive, however, carbon assimilation becomes restricted while nitrogen metabolic demand remains, potentially causing C-N imbalance and affecting plant dry matter accumulation and substrate supply for secondary metabolism. 5.3 Effects on the accumulation of flavonoids, polysaccharides, and phenolic compounds Flavonoids, polysaccharides, and phenolic acids are important active components for evaluating the medicinal quality of T. hemsleyanum, and they are also representative pharmacologically active substances in its tuberous roots and leaves (Hu et al., 2021). The accumulation of these components is jointly regulated by multiple factors, including light intensity, spectral composition, temperature, water availability, nutrient status, and growth stage. The shading environment can influence the operation of secondary metabolic pathways in T. hemsleyanum by altering light signal input, photosynthetic product supply, and cellular redox status. Moderate shading can alleviate strong light stress and maintain a relatively stable physiological metabolic state, thereby providing a favorable cellular environment for active component synthesis. Meanwhile, suitable weak light or specific light quality stimulation may also induce plants to adjust phenylpropanoid metabolism and flavonoid biosynthesis, thereby affecting the accumulation of flavonoids and phenolic compounds. Different active components do not respond uniformly to shading environments. In T. hemsleyanum cultivated under different colored films, blue film promoted vegetative growth and soluble amino acid accumulation, whereas red film significantly increased flavonoid content and the activity of key enzymes such as phenylalanine ammonia-lyase (PAL). This indicates that changes in light quality under shading environments may lead plants to exhibit different metabolic orientations between yield and quality (Bai et al., 2021). Long-term low-intensity blue light treatment of T. hemsleyanum tuberous roots can simultaneously increase tuberous root yield and total flavonoid content, enhance antioxidant activity, and upregulate genes related to flavanol biosynthesis (Zhao et al., 2024). In addition, seasonal analysis has shown that flavonoid content, as well as the antioxidant activities of major phenolic compounds and polysaccharides in T. hemsleyanum, fluctuate with changes in sunshine duration, temperature, and humidity, while suitable shading conditions help enhance the accumulation of medicinally relevant phenolic compounds and polysaccharides (Figure 2) (Shi et al., 2022). These results indicate that the accumulation of active components in T. hemsleyanumis sensitive to both light intensity and spectral composition, and shading management affects not only yield but also the intrinsic quality of medicinal materials. Polysaccharide accumulation is usually closely related to carbohydrate metabolism, tuberous root development, and storage substance formation. Therefore, when excessive shading causes carbon source insufficiency, polysaccharide accumulation may be inhibited. Shading studies on Bletilla species have shown that moderate shading or medium light intensity can result in relatively high polysaccharide content, accompanied by increases in precursor substances such as sucrose-6-phosphate and glucose-6-phosphate. In contrast, excessive shading or strong light reduces polysaccharide levels and disrupts carbon metabolism (Xu et al., 2024; Zhu et al., 2024). Flavonoids and phenolic compounds are more strongly affected by light signals, oxidative stress, and secondary metabolic enzyme activities. Studies on tea plants have shown that strong shading generally inhibits flavonoid and catechin biosynthesis while increasing free amino acid content, indicating that reduced light can alter the balance between nitrogen-rich and carbon-rich metabolites (Li et al., 2020; Shao et al., 2022). Therefore, the effects of shading environments on the medicinal quality of T. hemsleyanumare component-specific, light quality-sensitive, and intensity-dependent. An ideal shading regime should promote the coordinated accumulation of major active
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