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

Abstract

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 (Rd) to gross photosynthesis (Ag) were examined. The results showed that DROP treatments affected the Rd/Ag 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 Rd/Ag ratio in cucumber and tomato plants was entirely due to the rise in Rd. In the case of temperature drops to 8°C and below, the increase in Rd/Ag was determined by both elevation of Rd and the concurrent decrease in Ag. In cucumber plants, the extent of Ag and Rd 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 Rd/Ag 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.