The Effects Of Light On The Growth And Quality Of Lettuce In Plant Factories

The experiment was carried out in a closed artificial light plant factory,in hydroponic cultivation of"Red 1" lettuce(Lactuca saliva L.)as the experimental material.Research the effects of LED red and blue light,green light,far-red light and the corresponding light mode for lettuce dynamic growth,photosynthetic pigment,soluble sugar,crude protein,vitamin C and nitrate contents.The purpose of this paper was to elucidate the relationship between artificial light and lettuce growth and quality formation,and to provide theoretical and experimental basis for the establishment of high efficiency and low energy LED light supply strategy for lettuce in plant factory.The results of this study were:The experiment was carried out to improve the traditional mode of light,in the 16 h light period,by adjusting the on and off time of red and blue light for the formation of alternating 1 time(RB1),2 times(RB2),4 times(RB4)and 8 times(RB8)for four different light modes.The red and blue light were supplied with on light time 8 h(RB0')and 16 h(RB0)as the control.The treatments were the same intensity,red and blue ratio of 2:1.The results showed that RB1 treatment significantly increased the fresh weight,soluble total sugar and crude protein content of lettuce in RB1 compared with RB0'.RB4 treatment was beneficial to the accumulation of Vc and metabolism of nitrate.The contents of chlorophyll and carotenoid were the highest under RB8 treatment.The experiment by white light irradiation for 12 h(0:00-12:00)was used as the basal light to ensure the normal growth of lettuce.Two kinds of LED far-red light(peak at 850 nm and 930 nm)were used as supplemental light.Three modes of far-red light that were respectively semi-overlapped(S),overlapped(O)and non-overlapped(N)relative to the basal white light were applied by adjusting the on and off time of far-red light.That was,six treatments which were respectively Fr930S,Fr850S,Fr930O,Fr850O,Fr930N,and Fr850N had been examined in the study.The light intensity,lighting period as well as the electric energy consumption were the same among treatments.The results showed that 850 nm far-red light for light independent of white light was in favor of lettuce on fresh weight accumulation.The content of total soluble sugar and crude protein was the highest in 850 nm far-red light semi-overlapped mode.when the accumulation of Vc and nitrate metabolism of 930 nm far-red light was independent light.The experiment was carried out with 8:00-20:00 irradiation LED white light as the basal light and three different intensity of the green light(30,60,90 mol·m-2·s-1)as supplement light.Two modes were treated of which non-overlapped(N)and overlapped(O)by adjusting the on and off time of white light and green light.The six treatments were W,WG30N,WG90N,WG300,WG60O,WG90O,respectively.The white light intensity was the same among treatments.The results showed that the biomass of lettuce was the highest in WG30O treatment,and the content of total sugar,crude protein,Vc was the highest and the nitrate content was the lowest under WG90O treatment.Therefore,the purpose of vegetable production were to choose and to adjust precisely red and blue light frequency,far-red type and light intensity and light green mode in the actual production.