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Effects of short-term continuous lighting with LED lamps and nitrogen nutrition conditions on quality of hydroponically grown purple lettuce.

YU Yi, YANG Qi-chang, LIU Wen-ke   

  1. (Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences/Ministry of Agriculture Key Laboratory of Energy Conservation and Waste Management of Agricultural Structures, Beijing 100081, China)
  • Online:2015-11-18 Published:2015-11-18

Abstract: Purple lettuce was grown hydroponically under six different nitrogen nutrition conditions, with NO3--N:NH4+-N at 1:0, 4:1 and 1:1 combined with nitrogen application levels of 10 and 15 mmol·L-1, for 25 days in solar greenhouse, then treated with shortterm continuous lighting (SCL) before harvest to study the changes in contents of nutrients and analyze the effects of nitrogen nutrition conditions on the changes. Results showed that the shoot dry mass of all six nitrogen nutrition conditions were significantly improved under SCL treatment,  by 35.1% at least, and the root dry mass increased greatly except for NO3--N:NH4+-N 1:1 combined with nitrogen application level 15 mmol·L-1 treatment and NO3--N:NH4+-N 1:0 combined with nitrogen application level 10 mmol·L-1 treatment. The relative contents of total phenols and flavonoid of different nitrogen nutrition conditions turned significantly different after treatment with SCL. The relative contents of total phenols and flavonoid were enhanced with the improvement of ammonium nitrogen ratio, while the relative content of anthocyanin increased and then decreased with the improvement of ammonium nitrogen ratio. The lighting treatment reduced the nitrate content of leaf blade of all six nitrogen nutrition conditions remarkably  by 23.2% at least. The contents of ascorbic acid, soluble sugar and soluble protein rose significantly under SCL treatments. The study showed that the reduction of nitrate content speeded up with the enhancement of nitrogen application level and ammonium nitrogen ratio, and the advancement of ascorbic acid content slowed down with the increasing nitrogen application level. The soluble sugar improvement speed increased with the increasing ammonium nitrogen ratio, and SCL lifted the dry mass of the lettuce greatly. The results showed that SCL with LED lamps improved significantly the dry matter of lettuce under different nitrogen nutrition conditions, reduced the nitrate content and increased the ascorbic acid, soluble sugar and soluble protein contents greatly. In addition, nitrogen nutrition conditions affected the effectiveness of shortterm continuous lighting on quality improvement rate of hydroponic lettuce remarkably.