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Agronomy, Vol. 10, Pages 1678: Growth and Nutrient Element Content of Hydroponic Lettuce are Modified by LED Continuous Lighting of Different Intensities and Spectral Qualities
Agronomy doi: 10.3390/agronomy10111678
Authors: Wenke Liu Lingyan Zha Yubin Zhang
LED red (R) and blue (B) continuous light (CL) is a potential efficient way to increaseplant productivity of plant factory with artificial light (PFAL), but limited information wasexplored about their effects on plant mineral nutrition. In an environmentally controlled plantfactory with artificial light (PFAL), the effects of CL of different intensities and spectral qualities,emitted by R and B LEDs on growth and nutrient element content and accumulation of lettuce(Lactuca sativa L.), were conducted in three hydroponic experiments. Two treatments, normal light(12 h/12 h) and CL (24 h/0 h) in experiment 1, three CL intensities (100, 200 and 300 &mu;mol∙m&minus;2∙s&minus;1) inexperiment 2, and three CL light qualities (1R:3B, 1R:1B and 3R:1B) in experiment 3 weredesigned. The results showed that CL significantly increased the fresh and dry lettuce shootbiomass compared with normal light, and shoot fresh and dry biomass increased with theintensity increment of CL. In experiment 3, shoot fresh biomass was great under high R lightproportion CL treatment, while dry shoot biomass remained unchanged. Both CL and CL withincreased intensities promoted shoot C content and accumulation in lettuce. CL reduced N, P, K,Ca, Mg, Cu and Zn contents in lettuce shoot, while Fe and Mn contents did not change comparedto NL. Moreover, CL increased Ca, Fe and Mn accumulation. 100&ndash;200 &mu;mol∙m&minus;2∙s&minus;1 CL facilitatedN, P, Ca, Mg, Fe, Mn, Cu and Zn contents in shoot, but K content was not influenced comparedwith 300&mu;mol∙m&minus;2∙s&minus;1. The data showed that high B light ratio (75%) facilitated C contentcomparison with low B ratios (50% and 25%). However, lettuce grown under 3R1B treatment hadthe higher C accumulation. Shoot N, P, K, Ca, Mg, Fe, Mn and Zn contents were higher under1R1B treatment, and Cu content did not affected by light quality. Moreover, accumulation of N, P,K, Ca, Mg, Fe, Mn, Zn and Cu in shoot was higher under 1R1B treatment, while P, Ca, Mg, Mnaccumulation under 3R1B treatment was the lowest. In conclusion, CL tends to reduce shootmineral element contents due to dilution effect as shoot dry weight increases compared to NL.However, long‐term (12 days) CL composed of 1R1B, 100&ndash;200 &mu;mol∙m&minus;2∙s&minus;1 tends to obtain relativehigher K, Ca, Fe and Zn contents in the greater dry lettuce shoot.