The effects of LEDs on growth and morphogenesis of vegetable seedlings cultivated in growth chambers

The experiments with artificial lighting of vegetable seedlings using different type of lamps were carried out on tomato cultivar `Debut' and cucumber `Kafkas', in the period from November 2015 to January 2016. Seedlings were grown in growth compartments with controlled climate (temperature, light, photoperiod) and then in a greenhouse. For plant lighting the 400 W HPS lamps, and two variants of LED's lamps with the different participation of red (R) and blue (B) wavelength were used. LED I had R (640-660 nm) 54,6%; B (433-450 nm) 43,7%, FR (735 nm) 1,52% and LED II R (640-660 nm) 68,5%, B (433- 450 nm) 28,4% and FR (735 nm) 3,1%. Morphological measurements (plant height, fresh weight, leaf area), measurements of leaves greenness (index SPAD) and the measurement of leaf stomatal conductance were applied. The results indicate that varying lighting systems affected plant growth and quality of the vegetable seedlings. Tomato reacted differently than cucumber to the different light spectra. The use of LEDs allowed to obtain very good plant habit, especially in the first stage of cultivation. Tomato seedlings grown with HPS were the highest, however that grown with LED II had the highest fresh weight, highest leaf area and the best leaf coloration. Cucumbers grown with HPS lamps were characterized by a higher weight and larger surface of the leaves, and that lighted with LED I type lamps were taller and had a larger diameter. In turn, using the lamps LED II resulted in the best leaf coloration and plants were characterized by a high stomatal conductance. Higher fresh weight gain cucumber seedling grown under HPS lamps than that grown under the LED's, probably due to the effect of higher temperatures of the leaves, as HPS lamps emit more heat and cucumber has higher thermal requirements than tomato.