To investigate the effects of varying shading intensities on the growth and photosynthetic physiological characteristics of Cyphomandra betacea seedlings, clarify the optimal light intensity range for seedling growth, and to provide theoretical references and technical guidance for understory intercropping and intensive seedling production.

One-year-old Cyphomandra betacea seedlings were selected as experimental materials. Four shading treatments were established: full sunlight (CK, 100% natural radiation, NR), light shading (S₁, 75% NR), moderate shading (S₂, 50% NR), and severe shading (S₃, 30% NR). Growth and physiological indices including seedling height, ground diameter, single-leaf area and photosynthetic pigments content were measured. Correlation analysis and fuzzy membership function comprehensive evaluation were performed to elucidate the light adaptation mechanism of seedlings.

1) Seedling growth was significantly affected by shading treatments (P<0.05). In the S₁ treatment, seedling height increased by 10.5% compared with the CK group and exhibited the best leaf expansion performance, whereas the S₃ treatment significantly inhibited stem radial growth; 2) Photosynthetic measurements demonstrated that the S₁ treatment maintained a relatively high net photosynthetic rate (7.84 μmol·m^-2·s^-1), with a significantly higher non-photochemical quenching (NPQ) value (11 489.98) than the CK group. Moderate shading was proven to enhance the heat dissipation capacity and effectively alleviate leaf photoinhibition; 3) Correlation analysis showed that seedling height had an extremely significant negative correlation with net photosynthetic rate (r=-0.587, P<0.01), while stomatal conductance was extremely significantly positively correlated with net photosynthetic rate (r=0.731, P<0.01); 4) The fuzzy membership function evaluation results verified that the S₁ treatment was the optimal growth condition, with an average comprehensive value of 26 116.65.

Cyphomandra betacea seedlings can adapt to shading stress via morphological plasticity (plant height promotion and leaf area expansion) and photochemical efficiency regulation. In summary, 75% NR is identified as the optimal light condition for seedling growth, which can be applied to understory intercropping and shading-based intensive seedling cultivation.