Investigating LED lighting spectra to improve plant growth and energy use efficiency

The climate change, natural resource collapsing, the world population increase, and accompanied by the urbanization movements, are forging the global food security issue. Vertical farming as an agriculture mode in the urban areas is designed to meet the city food requirement as a priority, at the same time, the emergence of LED semiconductor light source not only provides an ideal controllable light source for plant cultivation, also offers a mythology for plant photobiology study. It qualified the LED light to be the option meeting the overall requirements for modern agricultural production mode, such as high efficiency, high yield, top quality, ecology and safety, which consequently engaged this lighting method with extensive application prospects. The research was mainly conducted with pak choi (Brassica rapa, Chinensis), to detect the difference physiological response and gene expression under treatments of the changed LED spectra. LED lighting can benefit the spectral output by becoming adjustable and species-specific for generating the appropriate 'light recipes' covering the plant consistently changing requirements, according to the growth stages, developing appeals and the species differences. This study exploits new developments in a low cost, efficiency, and new LED lighting system with the optimised set of wavelengths which needed to maximise yield with suitable trade-offs on energy input. In pak choi growth, the red/blue ratio as 70%/30% LED treatments showed positive effects on pak choi, as the yield can be increased by 50% compared with fluorescent lamp. Also, the LED lights showed remarkable improvement in energy saving and flexibility during production. In addition, the blue light shows significant affection for plant photomorphogenesis and light stress tolerance in mixed and monochromatic light. The CO2 absorption was also strongly regulated by the proportion of blue light, which indicate the fact that the ratio of red and blue light was the deciding factor in balancing light reaction and the Calvin cycle. The chlorophyll fluorescence measurements suggested 73% red / 27% blue ratio LED light recipe can increase the efficiency in PSII centre and carbon fixation which related to fresh matter increasing. Furthermore, a large number of differential expressed genes was detected by RNA-sequencing in pak choi, which showed genome-scale insight of gene expression responded under different light treatments