Effects of Elevated CO2 Levels on the Growth and Yield of Summer-Grown Cucumbers Cultivated under Different Day and Night Temperatures

Abstract

The effects of elevated CO2 (eCO2) levels on field-grown cucumbers have been extensively studied. However, the variations in photosynthate accumulation in summer-grown cucumbers simultaneously exposed to eCO2 and varying day-night temperatures (DNF) still remain unexplored. This study aimed to investigate the effects of DNF different CO2 conditions [ambient CO2 (aCO2; 400–600 μmol mol−1) and eCO2 (800–1000 μmol mol−1)] on dry matter production and dry matter distribution in summer-grown cucumbers under two DNF treatments (35/10 °C and 25/20 °C, day/night). We observed that long-term eCO2 exposure increased C assimilation and photosynthate accumulation in leaves, resulting in feedback inhibition of the leaf area. Under both DNF treatments, the total dry matter distribution to fruits under eCO2 conditions was approximately 15% higher than that under aCO2 conditions. Furthermore, soluble sugar content and C:N ratio increased with long-term eCO2 exposure, indicating increased C allocation, photosynthate accumulation, and distribution. However, low night temperatures (LT) inhibited respiration and increased dry matter accumulation by 30% under eCO2 conditions. Additionally, eCO2 increased fruit fresh weight by 8% and 12% under both DNF treatments compared to aCO2. This suggests that long-term eCO2 exposure and varying DNF exhibited different effects through different metabolic mechanisms on cucumber growth at high temperatures. eCO2 conditions probably increased dry matter distribution to improve fruit quality, and LT treatment altered the respiration rate to restore photosynthesis, thereby increasing photosynthate distribution to fruits. Therefore, a combination of CO2 enrichment and DNF can be used to improve fruit quality and yield at high temperatures.