Influence of Daily Short-Term Temperature Drops on Respiration to Photosynthesis Ratio in Chilling-Sensitive Plants

Cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), and sweet pepper (Capsicum annuum L.) plants were subjected daily over 13 days to short-term (2 h) temperature drops to 12, 8, 4, and 1°C (DROP treatments) at the end of night periods, and effects of these chilling treatments on the ratio of dark respiration in leaves (R_d) to gross photosynthesis (A_g) were examined. The results showed that DROP treatments affected the R_d/A_g ratio in leaves: this ratio increased significantly in cucumber and tomato plants and was slightly affected in pepper plants. When the temperature drops to 12°C were applied, the increase in R_d/A_g ratio in cucumber and tomato plants was entirely due to the rise in R_d. In the case of temperature drops to 8°C and below, the increase in R_d/A_g was determined by both elevation of R_d and the concurrent decrease in Ag. In cucumber plants, the extent of Ag and R_d changes increased with the DROP severity, i.e., with lowering the temperature of DROP treatment. The inhibition of photosynthesis by DROP treatment in cucumber plants was accompanied by the diminished efficiency of light energy use for photosynthesis and by the increase in the light compensation point. The elevation in R_d/A_g ratio in cucumber plants was accompanied by the decline in growth characteristics, such as accumulation of aboveground biomass, plant height, and leaf area. It was concluded that the R/A ratio is an important indicator characterizing the adaptive potential of chilling-sensitive plant species and their response to daily short-term temperature drops.