To explore the effects of different nitrogen, phosphorus, and potassium fertilizer levels on the photosynthetic characteristics, yield, and fruit quality of ‘Menguan 1’. and to provide reasonable fertilization recommendations for the cultivation of this variety in the eastern part of the northern Tianshan mountains in Xinjiang.

Six-year-old Xanthoceras sorbifolium ‘Mengguan 1’ trees grown in Xinjiang were used as the experimental materials. A “3414” fertilizer-response experimental design was adopted, in which nitrogen, phosphorus, and potassium were each assigned four application levels: 0 (no fertilization), 1 (50% of the conventional fertilization rate), 2 (the conventional fertilization rate), and 3 (150% of the conventional fertilization rate). The conventional fertilization rates were defined as 0.75 kg pure N plant^-1, 0.60 kg P₂O₅ plant^-1, and 0.20 kg K₂O plant^-1. On this basis, the effects of different N-P-K fertilization combinations on leaf photosynthetic characteristics, light-response parameters, fruit morphology, and seed yield were systematically evaluated. The rectangular hyperbolic model (RH), non-rectangular hyperbolic model (NRH), exponential model (EX), and modified rectangular hyperbolic model (MRH) were used to fit the P_n-PAR curve, and the photosynthetic parameters (P_n, T_r, C_i, WUE) and yield and quality were analyzed.

The MRH model provided the best fit, with the calculated AQY, LCP, R_d, P_nmax, and LSP being closest to the measured values. The application of conventional nitrogen fertilizer (N₂P₂K₂) significantly increased leaf P_n, while high potassium fertilizer (N₂P₂K₃) significantly enhanced the WUE of ‘Menguan 1’. Compared to the control (N₀P₀K₀), P_n increased by 57.01% and WUE by 93.62%. Regarding yield and fruit traits, the fertilization ratios of N₂P₂K₂ and N₂P₃K₂ increased the single-plant yield by 68.17% and 62.28%, respectively, compared to N₀P₀K₀. The former increased seed number, fruit diameter, single fruit weight, and single seed weight by 31.50%, 14.91%, 56.50% and 115.21%, respectively, while the latter increased oil content by 14.03%.

When the pure amounts of nitrogen, phosphorus, and potassium fertilizers were 413.54 kg/hm², 613.64 kg/hm², and 213.44 kg/hm², respectively, the photosynthetic characteristics, yield, and fruit quality of ‘Menguan 1’ could be effectively improved.