Abstract: 【Objective】Light serves as a pivotal environmental regulator in plant morphogenesis and physiological adaptation. In grape facility cultivation, particularly under rain-shelter systems, insufficient light frequently constrains photosynthetic efficiency and reproductive development. To address this limitation, spectral-modulated supplementary lighting emerges as a promising agronomic intervention. This study investigates the impacts of varied light qualities spectra on the ecophysiological responses of 'Shine Muscat' (Vitis labrusca × Vitis vinifera), with emphasis on foliar morpho-anatomical adaptations, stem elongation dynamics, photosynthetic performance indices, fruit biochemical profiles, and flower bud differentiation. The findings aim to establish a theoretical basis and practical guidance for optimizing supplementary lighting strategies in facility cultivation. 【Methods】Five-year-old rain-sheltered ‘Shine Muscat’ grape were used in this study. Four treatments were applied: red light (RL), white light (WL), a Redblue light 2:1 (RBL 2:1), and CK (no-light control). LED lamps (36 W, 640 nm) were installed 30 cm above the canopy and operated 12 hours daily (8:00-20:00) from April 11th to September 7th, 2023. Each treatment consisted of 10 vines with three replicates, separated by shading films. Leaf area, basal stem diameter, and internode length were measured on 20 randomly selected shoots per treatment after two months of treatment. Leaf area was calculated using the formula: area = long axis × short axis × π/4. For chlorophyll fluorescence parameters, leaves were dark-adapted for 20 minutes, then subjected to 1-second fluorescence induction using 3000 μmol/m²/s light. JIP-test analysis was used to calculate variable fluorescence (Vt) and its difference (ΔVt), along with other fluorescence parameters. During the fruit expansion stage, photosynthetic parameters were recorded on sunny days between 8:00 and 18:00 using a CIRAS-3 portable photosynthesis system. Measurements of Pn (net photosynthetic rate), Gs (stomatal conductance), Ci (intercellular CO₂ concentration), and Tr (transpiration rate) were taken at six time points (8:00, 10:00, 12:00, 14:00, 16:00, 18:00). For fruit analysis, 20 clusters were sampled for each treatment, and one berry from the top, middle, and bottom of each cluster was measured for longitudinal and transverse diameters using a vernier caliper. Total soluble solids (TSS) and titratable acidity (TA) were determined using a refractometer, with TA analyzed after 50-fold dilution. Upon completion of the supplemental lighting treatment, dormant buds at physiological maturity were sampled for molecular analysis. qRT-PCR analysis was conducted using SYBR Green chemistry, with VvActin1 (GenBank accession: XM_010655094.2) serving as the internal reference gene for normalization. Gene-specific primers were designed using Primer Premier 5.0 software, with amplification efficiency validated through standard curve analysis. Relative gene expression levels were calculated using the 2^(-ΔΔCt) method. For phenological assessment, the flowering rate was quantified as the ratio of inflorescence-bearing buds to total observed buds during the subsequent spring phenological phase. Bud sampling followed a randomized complete block design, with three biological replicates per treatment. 【Results】The results demonstrated that supplemental lighting, particularly the RBL 2:1 and RL treatments, significantly promoted leaf growth and expansion in grapes. The 2:1 treatment also markedly increased internode length in nodes 4-7 of new shoots. Both the RBL 2:1 and WL treatments showed significantly higher maximum photochemical efficiency of PSII (Fv/Fm) and maximum fluorescence (Fm) compared to other treatments. The PI abs under supplemental lighting treatments was significantly higher than the CK and shading treatment (ST). The 2:1 treatment exhibited significantly greater Po, TRO/CSm and ABS/CSm per unit leaf area compared to the control and other groups, whereas energy absorption per reaction center (ABS/RC) showed the opposite trend. In terms of photosynthetic characteristics, the daily variation of Ci, Gs and Tr was optimal in the RLB 2:1 group, followed by the WL group, both significantly higher than CK and ST. The RLB 2:1 group exhibited the fastest fruit growth rate, with single fruit weight significantly higher than other groups, and all the light treatments improved fruit shape. At maturity, the TSS content of fruits in the RBL 2:1 and WL groups reached the highest levels at 19.67% and 19.63%, respectively, while TA content showed no significant differences among treatments. Additionally, supplemental lighting positively influenced bud differentiation in the following year. The RBL 2:1 treatment notably advanced budburst timing and increased budburst rates. Moreover, key genes involved in the photoperiod pathway, such as VvGI and VvSOC1, were significantly upregulated in the RBL 2:1 and WL groups. 【Conclusion】In summary, supplementary lighting increased the shoot growth rate, leaf area, PI abs value, and Fv/Fm value of 'Shine Muscat' grape, enhancing light use efficiency. Simultaneously, the fruit quality, flower bud differentiation capacity, and the expression levels of light-responsive genes were also improved. This provides a solid theoretical foundation for the application of supplementary lighting technology under rain-shelter cultivation conditions.
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