Responses of growth, photosynthesis, and associated components to hypoxia at different light intensities in red leaf lettuce

Abstract

Plant growth and photosynthesis are strongly influenced by environmental factors. Oxygen gas is an important factor in photosynthesis, photorespiration, and respiration. In a previous study, we suggested that long-term hypoxia treatment affected leaf expansion and leaf nitrogen and carbon contents. In the present study, we measured the effects of long-term exposure to five O2 treatments (0.4, 2, 7, 10, and 21%) on plant growth, photosynthetic characteristics, and nitrogen, carbon, sucrose and phytochemicals content in red leaf lettuce grown under two light intensities (180 and 350μmol m−2 s−1). The leaf area of plants grown at 0.4 or 2% O2 was significantly smaller than that of plants grown at 21% O2. The specific leaf area of plants grown under hypoxia was significantly lower than that of plants grown at 21% O2. The net CO2 assimilation rate peaked at 7% O2. While total nitrogen content in leaf gradually increased with O2 concentration, total carbon and sucrose content in leaf gradually decreased with increased O2 concentration. Polyphenol content in plants grown under hypoxia was significantly higher than that of plants grown at 21% O2 under both light conditions. Anthocyanin content of plants grown at 0.4 or 2% O2 was significantly higher than that of plants grown at 21% O2. From these results, we infer that photosynthesis was at 7% O2 enhanced by inhibited photorespiration, and the interaction of O2 and light conditions was affected by the accumulation of polyphenol and anthocyanin.