Abstract:【Objective】 The study aims to investigate the impacts of supplemental UV-B radiation on the photosynthetic efficiency and fruit quality of strawberries under low UV conditions of facility environment, and to provide theoretical basis for enhancing the quality and productivity of protected strawberry cultivation . The facility mainly regulates the temperature to ensure the normal flowering and fruiting of strawberries. It is difficult to change the poor winter lighting conditions, and due to the influence of the greenhouse film, some of the light intake inside the facility is blocked, resulting in a significant decrease in sugar content, light flavor, and dull color of the facility's fruits. Improving the photosynthetic performance of strawberry leaves, assimilates synthesis and operation, and fruit sugar accumulation through improved light quality regulation facilities may become a possibility. 【Method】 In this study, Xuelixiang strawberries cultivated in a solar greenhouse were used as test materials. One fruit development cycle, UV-B irradiation was supplemented daily (8:30—10:00) at dose gradients of 0.2, 0.4, 0.6, and 0.8 W·m-2 for 1.5 hours, denoted as T1, T2, T3, and T4, respectively. Plants without UV-B supplementation were used as controls, denoted as CK. Relevant environmental indicators inside and outside the greenhouse, leaf resistance, leaf photosystem performance parameters, fruit quality, and key growth and development indicators were measured. 【Results】The results showed that the daily average intensity of UV-B in the greenhouse during the experiment was about 52% of that in the open air, with a difference of 0.55~1.13 W·m-2 compared to the open air. The difference was the largest before and after noon. Among the resistance related indicators, the levels of malondialdehyde and proline in T4 significantly increased compared to CK, while other treatments showed no significant changes; The soluble protein content of T2-T4 increased significantly compared to CK；There was no significant difference in relative conductivity between T4 and CK, indicating that all UV-B treatments did not cause significant damage to the leaves; During the period of UV-B supplementary light, Δ VJ and Δ VK on the OJIP curve of the leaves were less than 0, indicating that UV-B radiation accelerated the electron transfer efficiency on the receptor side of the PSII reaction center; But during the relatively high temperature period at noon (12:30—14:30), the OJIP curve of T4 undergoes severe deformation, with Δ VK and Δ VJ values rising above the benchmark zero line first, followed by T3, T1, and T2 gradually increasing. Among them, T4 has the largest increase and T2 has the smallest, indicating that PSII has been suppressed by light, T4 has the greatest degree of suppression, and T2 has the smallest; In the afternoon (14:30—16:30), as the temperature decreases, T1, T2, and T3 can recover quickly. At 16:30, they have dropped below the zero line, while T4 requires a longer time to recover. This also indicates that the UV-B effect has short-term persistence.The actual photochemical quantum yield of PSII in T1, T2, and T3, as well as the effective photochemical efficiency Fv '/Fm', photochemical quenching coefficient qP, and non photochemical quenching coefficient qN of PSII, were significantly higher than those of CK in most periods. Low dose radiation increased Fv/Fm (maximum photochemical efficiency of PSII) and Δ I/I0 (PSI activity), indicating that low-dose UV-B radiation effectively improved the light harvesting ability, light energy conversion efficiency, and PSI reaction center efficiency of PSII reaction centers; The apparent electron transfer rate (ETR) was significantly lower than that of CK, while the decrease in T3 and T4 was significantly greater than that of T1 and T2, indicating that the higher the UV-B dose, the more electrons were allocated to other pathways; The content of chloroplast pigments such as chlorophyll a, chlorophyll b, and carotenoids showed a trend of first increasing and then decreasing with the increase of UV-B dose, with T2 being the highest and the difference being significant. As the UV-B gradient increases, the net photosynthetic rate, stomatal conductance, and transpiration rate all first increase and then decrease, while the intercellular carbon dioxide concentration first decreases and then increases. The inflection point for all four is T2, and T1 and T3 are significantly different from CK, indicating that low to moderate doses of UV-B radiation are beneficial for improving leaf photosynthetic capacity. The fresh weight of T1 and T2 aboveground parts under low-dose radiation increased by 41.4% and 46.35% compared to CK (the same below), the dry weight increased by 19.4% and 15.28%, the single fruit weight increased by 11.23% and 24.9%, and the soluble solids increased by 11.85% and 25.7%. The soluble sugar content increased by 23.57% and 64.96%. The high-dose effect is not significant, indicating that low-dose UV-B radiation can increase the accumulation and optimize the distribution of plant dry matter, which is beneficial for improving fruit quality. 【Conclusion】 Under the experimental conditions, the efficiency, photosynthetic performance, and fruit quality of the photosystem were better than those of the CK at doses of 0.2 W·m-2 (T1), 0.4 W·m-2 (T2), and 0.6 W · m-2 (T3). The overall effect was best at 0.4 W·m-2 (T2), and no visible damage was observed in all treatments.
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