Effects of foliar fertilizer on photosynthetic characteristics and fruit quality of Xiangfu in Linzhi, Xizang

【Objective】Apple production is very important economically in Linzhi region. This study aimed to elucidate the effects of different foliar fertilizers on photosynthetic characteristics and fruit quality of 12-year-old Xiangfu apple trees in Linzhi, Xizang, in order to increase. productivity and improve fruit quality.【Methods】To meet the study's objectives, a precise experimental design was adopted. Twelve-year-old Xiangfu apple (Malus domestica) trees with consistent growth and health were chosen as materials. Nine foliar fertilizer treatments were devised, each targeting a specific nutrient: selenium at 1 mg ·L-1 (A1), 2 mg ·L-1 (A2), and 3 mg ·L-1 (A3); zinc at 0.17 g ·L-1 (B1), 0.34 g ·L-1 (B2), and 0.51 g ·L-1 (B3); and calcium at 0.18 g ·L-1 (C1), 0.36 g ·L-1 (C2), and 0.54 g ·L-1 (C3). Spray of water was used as control (CK). Fertilizers were applied during critical growth stages-young fruit stage, rapid fruit enlargement, and fruit maturity-using calibrated sprayers to ensure uniform application and mini-mize variability. After treatment, photosynthetic indicators were measured, including relative chlorophyll content (SPAD value), indicating leaf greenness and photosynthetic potential, and net photosynthetic rate (Pn), quantifying light energy conversion. Stomatal conductance (Gs) and transpiration rate (Tr) were also assessed to understand water use efficiency and gas exchange. Fruit quality parameters were evaluated alongside photosynthetic assessments, including single fruit mass, solid-acid ratio, vitamin C content, soluble sugar content, fruit firmness, and titratable acid content.【Results】The application of foliar fertilizers yielded significant improvements in the photosynthetic characteristics of the apple leaves compared with the control. Specifically, the SPAD value, Pn, Gs, and Tr were all markedly increased. A ranking of the total scores of photosynthetic indicators for the different fertilization treatments revealed that B3 (zinc spraying at 0.51 g ·L-1 ) was the most effective, followed by A1 (selenium spraying at 1 mg · L- 1 ) and A3 (selenium spraying at 3 mg · L- 1 ). This indicated that treatments B3, A1, and A3 were particularly adept at promoting the physiological growth and photosynthetic efficiency of Xiangfu apple. Furthermore, the foliar fertilizer treatments had a pronounced impact on fruit quality. The single fruit mass, solid-acid ratio, vitamin C content, and soluble sugar content were all significantly enhanced, while fruit firmness and titratable acid content were reduced. To comprehensively evaluate the fruit quality under different treatments, principal component analysis (PCA) was conducted. The results of the PCA indicated that the treatments could be ranked according to their comprehensive scores as follows: A3＞B1＞C2＞A2＞A1＞C1＞C3＞B3＞B2＞CK. This suggested that while B3 was superior in promoting photosynthetic characteristics, A3 (selenium spraying at 3 mg · L- 1 ) demonstrated the most optimal overall effects on fruit quality.【Conclusion】The findings would highlight the strategic use of foliar fertilizers to enhance photosynthetic efficiency and fruit quality in Xiangfu apple. Improvements in SPAD, Pn, Gs, and Tr underscored the potential of foliar fertilization to optimize light capture, carbon fixation, and water use efficiency. Enhanced fruit quality parameters underscored the nutritional and commercial benefits of these fertilizers. A3 (selenium at 3 mg · L- 1 ) emerged as the most effective treatment, suggesting that selenium would be pivotal at optimal concentrations. Future research could explore the physiological and molecular mechanisms underlying foliar fertilizer effects, including nutrient uptake, assimilation, and interactions with endogenous hormones. Research could also investigate synergistic effects of combining different foliar fertilizers or integrating them with other agricultural management practices. Economic feasibility and cost-effectiveness evaluations would provide farmers with practical information on investment returns and guide technology adoption in practice.