Effect of Day and Night Temperature on Red Russian Kale Mineral Nutrient, Vitamin C, and Fiber Content

Red Russian Kale plants (Brassica napus var. pabularia) were germinated in a 24 °C /13 °C (day/night) greenhouse under an eight-hour photoperiod and were then moved to controlled environmental growth chambers maintained to achieve a 10 °C , 15 °C , 20 °C , 25 °C, and 30 °C leaf temperature after four true leaves had unfolded.  Plants were moved among chambers at 0800 and 1600 HR daily to yield a total of 25 day/night temperature regimes. Irradiance was maintained at 300 µmol·m^-2·s^-1 and plants were fertilized with 15–5–15 Cal-Mag fertilizer twice a week (400 ppm N) and watered as needed otherwise. The experiment was replicated four times in time. After 56 d, plants were removed from growth chambers and leaf number per plant was counted, individual leaf fresh and dry weight were determined (fifth leaf from bottom of stem), and foliar nutrients (P, K, Ca, Mg, Fe, Mn, B, Cu) were determined using an inductively-coupled plasma spectrophotometer. Total dietary fiber and vitamin C levels were also measured from tissue frozen at –80 °C for the pooled triplicate samples analyzed. Vitamin C levels were highest (46.9 mg/100g) and lowest (14.1 mg/100g) for the plants maintained at 15 °C /20 °C and 10 °C /30 °C (day/night) temperature, respectively. Plants maintained under a 30 °C night temperature had the lowest fresh weight, and in most regimes, significantly lower vitamin C content. Results indicated that for optimal growth (fresh weight) and leaf vitamin C content, day temperatures should be maintained between 15 °C and 20 °C and night temperatures between 15 °C and 25 °C . Day/night temperature regime effects on fiber and leaf mineral content will also be discussed.