Aplications of Laser Induced Chlorophyll Fluorescence Imaging to detect Environmental Effect on Spinach Plant

Abstract

Laser Induced Chlorophyll Fluorescence spectroscopy has been developed and used for many years and recently becomes a promising nondestructive method to detect early symptoms of environmental stresses on plants. An affordable, portable, and effective system of Laser Induced Chlorophyll Fluorescence detection needs to be developed that can be used by most farmers. In this research, a system of chlorophyll fluorescence imaging which consisted of some light sources, some optical components, samples, a CMOS camera as a detector has been applied to detect the effect of sunlight intensity variation on plants of Amaranthus tricolor spinach. The spinach plants were treated by the sunlight intensity variation after 10 days growth. The samples were the detached spinach leaves grown under three sunlight intensity variations and the spinach leaf extract in ethanol grown under two sunlight intensity variations. The detached leaf samples were taken for investigation after 10 days and 18 days treatments. There were 5 plant samples for each treatment. The spinach extraction samples was taken from different spinach plants after 20 day treatment. The variations of sunlight were 90 % using one layer of plastic cover, 40% using a layer of plastic and a layer of dark net cover, and 32 % using two layers of dark net cover, compared to sunlight intensity without cover. Diode lasers and LEDs with different wavelength were used as light sources, performances of both were compared. The detached leaves and the spinach extract in a cuvette were illuminated by laser and LED light and their images were recorded by the CMOS camera. The fluorescence intensities were represented by the maximum intensities of RGB values found from RGB plot using ImageJ software. The research results showed that wavelength diode lasers and LEDS that can give significant differences in the three treatments were 680 nm for LED and 780 nm for diode laser for detached leaf experiment. The 680 nm LED and the 780 nm diode laser, respectively, gave 24.3 % and 29 % different in fluorescence intensities between 90% and 32 % sunlight intensity treatments. The 525 nm LED and 532 nm diode laser did not give significant difference for all treatments. The fluorescence intensities were higher for 525 nm LED 532 nm diode laser than those for 680 nm LED and 780 nm laser because the chlorophyll absorbed more light in NIR wavelength. The fluorescence intensities were higher at 10 day treatment that at 18 day treatment. It could be because the plants had much less chlorophyll since the optimum growth of the spinach is 25 days. The leaf extract method gave better spectrum visualization however it could not differentiate both treatments significantly except at 680 nm wavelengths. Both diode laser and LEDS have the possibilities to be used as the low cost light source for chlorophyll fluorescence imaging.