Objective   Effects of CO₂ and LED exposure on the photosynthesis and quality of chili peppers in a solar greenhouse were studied.

  Method  In a two-way random zone group experiment, Huamei 105 chili pepper plants were exposed to natural light (L1), natural light supplemented with LED of R ∶ B=5 ∶ 1 (L2) or R ∶ B ∶ W=3 ∶ 2 ∶ 1 (L3), CO₂ at the natural 400±50 μL·L⁻¹ (C1) or at 800±50 μL·L⁻¹ (C2) in 6 combination treatments ∶ L1C1 (control), L1C2, L2C1, L2C2, L3C1, and L3C2. The physiological and photosynthetic characteristics of the plants under the treatments were compared.

  Result  The added CO₂ in the atmosphere as in C2 and supplementation of LED as in L2 and L3 increased the plant height and stem girth which were shown the significantly higher average height of 88.33cm and 93cm and girth diameter of 12.00mm and 13.34mm under L2C2 and L3C2, respectively, than higher CK treatments. Of all treatments, L2C2 produced the highest contents of chlorophyll a, chlorophyll b, and total chlorophyll as well as the greatest photosynthetic rate (P_n) that was 36.70% higher than control. Both L2C2 and L3C2 resulted in higher contents of vitamin C, soluble sugars, and soluble proteins in the chili peppers.

  Conclusion  Supply of added CO₂ and supplementation of LED light effectively improved the photosynthesis and pepper quality of the plants. The combined applications of L2 and C2 appeared particularly attractive for the local solar greenhouse chili pepper cultivation in winter.