Technical Foundation Of Environmental Feedback Control Of Hydroponic Lettuce Based On Photosynthesis Simulation

Plant factory with artificial light is a technical innovation for horticultural engineering.It is an important solution for solving agricultural product safety problems and improving facility benefit,and therefore to achieve clean and high-efficiency production.Light-emitting diode（LED） lighting with the advantages of energy-saving,high lighting efficiency,and adjustable spectral property as an alternative of fluorescent lamps are becoming to widespread use in plant factory.Although Japan has more than 200 commercial production of plant factory with artificial light,but half of them are still in a loss or flat state,many people attributed it to high energy consumption and low efficiency.In order to achieve LED lighting control and application of speaking plant approach to environment control（SPA）for hydroponic lettuce（Lactuca sativa L.）production in plant factory,environmental photosynthetic response models were developed based on effect experiments of LED light and temperature-light environment on growth and quality of hydroponic lettuce,and explored to environmental feedback control.In this paper,hydroponic production of purple lettuce（cv.Ziwei）was used to apply in the environment photosynthetic response models for applying SPA application in plant factory.The main results and conclusion are as following:1)In the effect experiment of light environment on growth and quality of hydroponic lettuce,leaf fresh weight and dry weight increased linearly when daily light integral increased,there were no significant differences in nitrate,soluble sugar,and vitamin C contents between treatments of light intensities of 250 and 300 μmol·m^-2-s^-1 with a photoperiod of 16 h·d^-1 at 16 days after transplanting.It was proved by continuous measurements of net photosynthetic rate of lettuce leaves at two days before harvest The great quality of lettuce was showed in treatments of LED lamps with R:B ratio of 2.2 compared to the LED lamps and fluorescent lamps with R:B ratio of 1.2 and 1.8.Higher light use efficiency of hydroponic lettuce was showed under LED lamps compared to fluorescent lamps.Therefore,light intensity of 250 μmol·m^-2·s^-1 with a photoperiod of 16 h·d^-1 under LED lamps with R:B ratio of 2.2 is suggested to apply for LED lighting control in hydroponic lettuce plant factory.2)To investigate effects of temperature and light intensity on growth and quality of hydroponic lettuce,fresh weights over 100 g plant^-1 were harvested at day/night temperature of 22/18℃ and light intensity of 250 μmol·m^-2·s^-1,and the soluble sugar,soluble protein and vitamin C contents were no difference compared to that under light intensity of 300 μmol·m^-2·s^-1.The leaf dry weights in treatments of T26-P300 and T22-P250 were significantly higher compared to the same light intensity with other temperature treatments.Therefore,day/night temperature of 22/18℃with light intensity of 250 μmol·m^-2·s^-1 were recommend for hydroponic lettuce production in plant factory with artificial lighting.3)Via model simulation and experimental verification of lettuce photosynthesis response to light,CO₂ concentration,and temperature,modified rectangular hyperbola models were suitable to fit photosynthetic response curves of light and CO₂ concentration,photosynthetic parameters calculation,and photosynthetic physiological interpretation.Compared to light intensity of 300μmol·m^-2·s^-1,higher light use efficiency of 0.052 to 0.055 of hydroponic lettuce production were found at light intensity of 250 μmol·m^-2·s^-1.Environmental photosynthetic response models developed in this study were performed well to simulate net photosynthetic rate from environmental combination of light intensity,CO₂ concentration,and temperature.Therefore,the photosynthetic model is available to use in environmental feedback control based on SPA technology for hydroponic lettuceplant factory.Further research will be needed because of time limited in this study.