Spectral Quality of Supplemental Led Grow Light Alters Chilling Tolerance in Ornamental Plants

Abstract

The spectral properties of light changes the direction and intensity of metabolic processes in the plant, which allows it to adapt to changing environmental conditions. The influence of the spectral properties of light on plant physiology is still not fully understood, and a significant part of the research is devoted to the short-term effects of processing with monochromatic light in growth chambers. The purpose of this study was to determine whether the spectral modifications of additional LED lighting in greenhouse production can alter the characteristics of ornamental plants after growing, which is susceptible to chilling injuries. We grew snapdragons (Antirrhinum majus nanum L.)  cv. Flora Shower White, tagetes (Tagetes patula L.) cv. Karmen, and multi-flowered petunia (Petunia hybrida L.) cv. Mambo blue in greenhouse conditions, using two different additional methods of irradiation with LEDs: 100 % red (l = 600 nm) (RL variant) and 100 % blue (l = 400 nm) (BL variant), followed by modeling the effect on the seedling of short-term cooling. The plants studied in the experiment are often used in urban landscaping and are exposed to low positive and zero temperatures, especially in the first days after transplanting into open ground. Morphological indicators and levels of hormonal regulators (salicylic acid (SA) and abscisic acid (ABA)) and water-soluble sugars, as well as changes in the selective permeability of cell membranes, were determined at the end of the exposure period. Light treatment showed a noticeable effect on the resistance of seedlings to cooling. Short-term exposure to low temperatures caused a violation of the semipermeability of cell membranes in all experimental variants, but it was minimal in plants under exposure to spectral light: the electrolyte yield decreased by 50 % in comparison with the control in petunias, up to 37 % in snapdragon and up to 37 % in tagetes eighteen %. In the test variants, after cooling, the yield of potassium ions and the content of salicylic acid decreased – by 9 and 14 % (RL) and 21, respectively, by 37 % (BL), and the content of water-soluble monosugars increased. After cooling, tagetes quickly restored turgor in the RL variant, but in the control and when using BL this process was slowed down, there was damage on the leaf edges. Plants of snapdragons and petunias under illumination (RL and BL) quickly recovered, they maintained a habitus close to the original, and budding began. In control plants, restoration proceeded more slowly; their decorative qualities were low. When transplanted into the open ground (at night temperatures of 2–5 °C), the survival rate of ornamental plants after exposure was 80–100 % versus 60–70 % in the control. Additional illumination with narrow-spectrum light when growing seedlings of ornamental plants can reduce the death of plants from spring frosts.