Abstract: Taking winter wheat Triticum aestivum L. (cv.Yangmai 13) as test material, a field experiment was conducted in Nanjing City to study the effects of simulated reduced solar radiation on the diurnal variation of winter wheat flag leaf photosynthetic rate and the main affecting factors. Five treatments were installed, i.e., 15% (T₁₅), 20% (T₂₀), 40% (T₄₀), 60% (T₆₀), and 100% (CK) of total incident solar radiation. Reduced solar irradiance increased the chlorophyll and lutein contents significantly, but decreased the net photosynthetic rate (P_n). Under different solar irradiance, the diurnal variation of P_n had greater difference, and the daily maximum P_n was in the order of CK＞T₆₀＞T₄₀＞T₂₀＞T₁₅. In CK, the P_n exhibited a double peak diurnal curve; while in the other four treatments, the P_n showed a single peak curve, and the peak was lagged behind that of CK. Correlation analysis showed that reduced solar irradiance was the main factor affecting the diurnal variation of P_n, but the physiological parameters also played important roles in determining the diurnal variation of P_n. In treatments T₆₀ and T₄₀, the photosynthesis active radiation (PAR), leaf temperature (T_l), stomatal conductance (G_s),and transpiration rate (T_r) were significantly positively correlated with P_n, suggesting their positive effects on P_n. The intercellular CO₂ concentration (C_i) and stomatal limitation (L_s) had significant negative correlations with P_n in treatments T₆₀ and T₄₀ but significant positive correlations with P_n in treatments T₂₀ and T₁₅, implying that the C_i and L_s had negative (or positive) effects on P_n when the solar irradiance was higher (or lower) than 40% of incident solar irradiance.

Key words: reduced solar radiation, winter wheat, diurnal variation of photosynthesis