Effects of short light/dark cycles on photosynthetic pathway switching and growth of medicinal Dendrobium officinale in aeroponic cultivation

Dendrobium officinale has high medicinal value but grows slowly in natural environment due to its special CAM photosynthetic pathway.In this study,D.officinale were grown aeroponically with light/dark cycles of 12 h/12 h,4 h/4 h,and 2 h/2 h for 150 d.The photosynthetic electron transfer characteristics,photosynthetic CO_(2) fixation pathways,and accumulations of biomass and soluble polysaccharides in D.officinale leaves were studied.The results showed that the photosynthetic apparatus states of D.officinale in aeroponic cultivation under short light/dark cycles of 4 h/4 h and 2 h/2 h were better than that under 12 h/12 h.The dark net CO_(2) exchange percentages of D.officinale were negative in short light/dark cycles of 4 h/4 h and 2 h/2 h,and the daily net CO_(2) exchange amount and dry/fresh weight increases were doubled compared with those in 12 h/12 h light/dark cycle.High soluble polysaccharides content and the soluble polysaccharides yield of D.officinale were obtained in the shorter light/dark cycle of 2 h/2 h.Therefore,the photosynthetic pathway of D.officinale could be switched from CAM to C3 by short light/dark cycles of 4 h/4 h and 2 h/2 h,and its higher biomass accumulation and soluble polysaccharides yield could be obtained by the shorter light/dark cycle of 2 h/2 h in aeroponic cultivation.

Effects of LED light quality on the growth of pepper seedling in plant factory

The extensive environment,especially low temperature and weak lighting in winter and spring,which limits the growth of pepper(Capicum annuum L.)seedlings,the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings.In this study,white LED lamps with R:B ratio of 0.7(L0.7)and 1.5(L1.5)and red-blue LED lamps with R:B ratio of 3.5(L3.5)were used to cultivate seedlings of“CAU-24”pepper in the light intensity of 250μmol/m^(2)·s and photoperiod of 12 h/d,white fluorescent lamps with R:B ratio of 1.7(F1.7)was used as control.The results showed that plant height,stem diameter,hypocotyl length,biomass accumulation,light energy use efficiency(LUE)and electric energy use efficiency(EUE)of pepper seedling under L1.5 were the highest.After 36 days of sowing,the dry weight of shoot reached 302.8±45.2 mg/plant.Leaf area reached maximum value of 153.5±22.0 cm^(2) under L0.7.The contents of chlorophyll a,chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7,but there was no significant difference in net photosynthetic rate.The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h)which was 1.5,2,and 3 times greater than that of L3.5,L0.7,and F1.7,respectively.Therefore,compared with fluorescent lamp and other LED lamps,the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency,greater LUE and EUE.

Optimal red:blue ratio of full spectrum LEDs for hydroponic pakchoi cultivation in plant factory

Pakchoi,a popular leafy vegetable in China,is expected to be planted in plant factories with artificial lighting(PFALs).In order to examine the effects of different red and blue light ratios(R:B ratio)on growth,photosynthesis,and absorption spectrum of plant leaves,and to analyze the energy use efficiency,the pakchoi(Brassica Chinensis L.cv.Xiazhijiao)was cultivated hydroponically under white LEDs with R:B ratios of 0.9(L0.9)and 1.8(L1.8),white plus red LEDs with R:B ratios of 2.7(L2.7)and 4.0(L4.0)for 40 d,respectively.The results showed that the leaf length and width were significantly greater in the L0.9 treatment than in other treatments,and the dry weight per plant increased by over 33%when R:B ratio decreased from 4.0 to 0.9.The net photosynthesis rates of pakchoi leaves ranged from 9.2 to 9.6μmol/(m2·s)under different lighting conditions,which had no significant difference.The biggest difference in the spectrum absorptance of pakchoi leaves was expressed in green light waveband,and the highest absorption of plant leaves was under L0.9 and L1.8 treatments.The light energy use efficiency(LUE),photon yield(PY),and energy yield(EY)in L0.9 were over 25%higher than that in the other treatments,while there was no significant difference in the electrical energy use efficiency(EUE).In conclusion,an optimal light quality to cultivate pakchoi in PFALs was the white LEDs with R:B ratio of 0.9,and this finding could provide a promising lighting environment to hydroponic pakchoi yield and energy use efficiency.