Single And Combined Effects Of Temperature And Red:Far-Red Light Ratio On Evening Primrose (Oenothera Biennis)

Few studies have considered the interactive effects of temperature and red: far-red light ratio (R:FR) on plants. We studied the effects of these two factors on evening primrose (Oenothera biennis L.). Plants were grown under two temperature regimes (22 degrees C day - 18 degrees C night and 28 degrees C day - 24 degrees C night) and two R:FR light ratios (low, simulated shade FR enrichment and normal, simulated natural sunlight) in controlled-environment chambers and their growth and physiological characteristics were measured. Among the 23 parameters, 20 were affected by temperature, 21 were affected by light quality, and 16 were affected by their interactions. Higher temperatures increased stem height, photosynthetic pigments, and ethylene, but decreased gas exchange and, in turn, plant biomass. Low R:FR increased stem height, transpiration, stomatal conductance, and ethylene, but decreased photosynthetic pigments, water-use efficiency, and photosynthesis and, in turn, plant biomass. Distinct parallel patterns were found for the combined effects of temperature and light quality. Plants had 2.3 times lower total biomass under lower temperatures at low R:FR than under the same temperatures at normal R:FR. However, plants had 2.8 times lower total biomass under higher temperatures at low R:FR than under the same temperatures at normal R:FR. We conclude that the interactive effects of temperature and R:FR are different than that of the single factors on the natural populations of O. biennis.