Objective To evaluate the comprehensive performance of fruit quality and leaf functional traits among different Corylus heterophylla × C. avellana cultivars, reveal the synergistic relationship between them, and provide a theoretical basis for the early selection of high-quality cultivars.

Method Six hybrid hazelnut cultivars (‘Dawei’, ‘Liaozhen 3’, ‘Liaozhen 7’, ‘Liaozhen 8’, ‘Yuzhui’ and ‘B21’) in Northeast China were used as materials to determine their fruit economic traits, nutritional quality, and leaf functional traits. One-way analysis of variance was used to compare trait differences among cultivars, and the entropy-weight TOPSIS method was applied to comprehensively evaluate the fruit quality of different cultivars. Furthermore, redundancy analysis and correlation networks were employed to elucidate the relationships between leaf functional traits and fruit traits.

Result (1) Significant synergistic differentiation was observed in fruit quality and economic traits among cultivars. ‘Yuzhui’ performed best in core indicators such as fat, soluble sugar, and kernel ratio, ranking first in comprehensive score, followed by ‘Liaozhen 8’; whereas ‘B21’ had the lowest economic conversion efficiency and overall score due to excessive investment in shell structure. (2) RDA and network analysis revealed that Chl, SLA, and P contents were significantly positively correlated with fruit quality, indicating that higher photosynthetic potential effectively promotes nutrient deposition. Conversely, NSC content was significantly negatively correlated with quality and served as a core indicator in the network; its high accumulation in leaves suggested low carbon mobilization efficiency and restricted assimilate transport. (3) High-quality cultivars exhibited a functional combination of "high Chl–large SLA–low NSC," reflecting strong resource acquisition and carbon export capacities. In contrast, low-scoring cultivars tended toward higher NSC accumulation and structural investment, which limited nutrient deposition in the fruit edible parts.

Conclusion The differentiation of fruit quality in C. heterophylla × C. avellana is primarily influenced by leaf carbon allocation strategies. Low NSC, high chlorophyll, and large specific leaf area can serve as reliable physiological indicators characterizing the highly efficient carbon mobilization capacity of the plants, providing an important basis for the early identification of elite germplasms and the selection of high-quality hybrid hazelnut cultivars in the future. Integrating fruit traits and leaf physiological functions, ‘Yuzhui’ and ‘Liaozhen 8’ possess the excellent synergistic characteristics of “high photosynthetic acquisition—high carbon output” and exhibit the best comprehensive quality performance, which recommended to prioritize these two cultivars as guiding varieties in the future production practices and promotion of high-quality hazelnut orchards.