Improving energy efficiency, germination indices and root system development in Cape periwinkle and marigold through spectral distribution and light exposure time

Lighting systems in controlled environment agriculture affect the economic sustainability of plant production by electricity consumption. The purpose of this experiment was to investigate the possibility of reducing the electric power consumption required for Cape periwinkle (Catharanthus roseus L. cv. Titan rose halo) and marigold (Tagetes erecta L. cv. Antigua orange) seed germination by changing the combinations of light spectra and light exposure time, and to improving energy use efficiency at seedling stage and photomorphogenesis of roots by changing spectral distribution and daily light integral (DLI). For this purpose, an experiment using various combinations of blue476nm and red625nm spectra together with broad-spectrum lamps including Fluorescent as control, high pressure sodium and white LED lights in varying light exposure times were performed. Marigold showed maximum seed germination under 2 h of red625nm light and so that Cape periwinkle under 4 h of 70 % R625nm: 30 % B476nm. The results revealed that the modification in the spectral distribution reduced the total time to achieve maximum germination, thereby diminishing the electricity consumption. Increasing DLI, irrespective of spectral distribution, resulted in a decrease in the shoot length of the marigold, but roots showed a reverse pattern. Cape periwinkle showed the same pattern except for those under 55 % R625nm: 45 % B476nm, which needed less DLI to achieve the highest root length. Combinations of blue476nm and red625nm LEDs had better energy use efficiency than control or any other broad-spectrum lamps to produce one-milligram dry matters of the shoot and root. Increasing DLI had positive effect on the number and longitudinal growth of lateral roots, and increasing blue476nm light percentage reduced their number. This study demonstrated that it was possible to increase the germination indices, control root photomorphogenesis more precisely and improve energy use efficiency by changing light combination spectra compared to broad-spectrum lamps.

Automated summary

By changing the combinations of light spectra and light exposure time, it is possible to reduce electricity consumption for seed germination, enhance energy use efficiency, control root photomorphogenesis, and increase the number and longitudinal growth of lateral roots.