Effects Of Light And Nitrogen Coupling Regulation On Growth And Quality Of Hydroponic Lettuce

Lettuce is a kind of leafy vegetable widely used by people.It is also a representative vegetable widely planted in artificial light plant factory.High nitrogen hydroponics is usually used in lettuce production in plant factories.The yield of lettuce could be greatly increased under high nitrogen condition.But the nutrient content represented by AsA is relatively low.AsA content in lettuce is closely related to nitrogen supply and light conditions.There is interaction between carbon and nitrogen metabolism and light environment.The results showed that the nutritional quality of hydroponic leafy vegetables could be significantly improved by a certain intensity of short-term continuous light before harvest.In this study,LED red and blue light were used for short-term continuous pre-harvest light treatment during the growth of hydroponic lettuce to improve the quality of lettuce.At the same time,explore how nitrogen supply conditions and pre-harvest LED short-term continuous lighting conditions can be coupled to play the best synergistic effect and achieve high-quality and high-yield hydroponic lettuce.This study mainly studied the mechanism of AsA content and related metabolic network changes in hydroponic lettuce under different light intensities and nitrogen levels and its response mechanism to continuous light before harvest in an artificial light plant factory with controllable environment.The effects of hydroponic nitrogen nutrition and light environment conditions and continuous pre-harvest light on lettuce growth,nutrient element content,AsA content and AsA anabolic key enzyme activities were mainly studied.The main research results and research conclusions are as follows:1.The lettuce was treated with different light intensity(100,150,200,300 and 500?mol·m^-2·s^-1)and the same ratio of red and blue light quality?4R:1B?for 72 hours before harvesting.The effects of continuous light intensity before harvest on hydroponic lettuce growth,nutrient element content,AsA content,and AsA anabolic key enzyme activity were studied.The results showed that the yield,soluble sugar and As A content of Hydroponic Lettuce increased gradually with the increase of continuous light intensity.High light intensity treatment(500?mol·m^-2·s^-1)can significantly promote the accumulation of C,N,Fe and Zn in lettuce.The increase of AsA content was due to the enhancement of continuous light intensity,which increased the activities of MDHAR?DHAR and GR enzymes involved in AsA regeneration cycle.2.Before harvesting,the lettuce was continuously irradiated with red blue light for 72 hours with different light quality ratios?1R:4b,1R:2B,1R:1B,2R:1B and 4R:1B?and the same light intensity of 150?mol·m^-2·s^-1.The effects of continuous light quality before harvest on growth,nutrient element content,AsA content and key enzyme activity of AsA synthesis and metabolism of lettuce were studied.The results showed that the yield and soluble sugar content of lettuce increased with the increase of the ratio of red light to continuous light.The content of AsA increased gradually with the increase of the proportion of continuous blue light.The increase of ASA content was due to the increase of the ratio of continuous light to blue light,which increased the activity of MDHAR.3.In the experiment,8,10,12 mmol/L high nitrogen level treatment was set up,the light intensity was 150?mol·m^-2·s^-1,the red blue light ratio was 4R:1b,and the light period was 16/8 h.On the 18th day after planting,72h continuous light treatment with a light intensity of 150?mol·m^-2·s^-1,red and blue qualities of 2R:1B and 4R:1B,respectively.The effects of different high nitrogen levels on hydroponic lettuce growth,nutrient element content,AsA content and AsA anabolism key enzyme activity and the response to continuous light quality before harvest were studied.The results showed that high nitrogen levels?8-12 mmol/L?inhibited the increase of hydroponic lettuce yield and AsA content.After continuous illumination,lettuce yield,soluble sugar and AsA content increased significantly.The treatment of 72h continuous light with 4R:1b of red and blue light was beneficial to obtain higher nutrient content and accumulation under the premise of high nitrogen level.The significant increase of AsA content was due to the increase of the ratio of red light to continuous light and the level of nitrogen,which increased the activities of Gal LDH and DHAR enzymes involved in AsA synthesis and metabolism.