Ratio of Intensities of Blue and Red Light at Cultivation Influences Photosynthetic Light Reactions, Respiration, Growth, and Reflectance Indices in Lettuce.

Abstract

Simple SummaryIllumination is an important factor for plant life because light is the basis of photosynthesis and productivity, the regulator of physiological processes, and a potential cause of damage. The development of LED technology has contributed to increasing the efficiency of illumination during plant cultivation through the use of light sources with narrow spectral bands. However, the characteristics of influence of light sources with different spectra on specific species of agricultural plants require further investigation. In the present work, we analyzed the influence of two variants of LED illumination (with increased intensity of red or blue light) on physiological processes in lettuce. These variants were selected because they corresponded to two maximums of photosynthetic light absorption. It was shown that, under the increased intensity of the blue light, both respiration and cyclic electron flow were stimulated; theseprocesses are known to be related to stress changes in plants. In contrast, under the increased intensity of the red light, linear electron flow was stimulated, a process that is related to plant productivity, and the biomass during cultivation was increased. The reflectance of leaves was also dependent on the variant of illumination. In the future, our results can be used to increase the efficiency of lettuce cultivation.LED illumination can have a narrow spectral band; its intensity and time regime are regulated within a wide range. These characteristics are the potential basis for the use of a combination of LEDs for plant cultivation because light is the energy source that is used by plants as well as the regulator of photosynthesis, and the regulator of other physiological processes (e.g., plant development), and can cause plant damage under certain stress conditions. As a result, analyzing the influence of light spectra on physiological and growth characteristics during cultivation of different plant species is an important problem. In the present work, we investigated the influence of two variants of LED illumination (red light at an increased intensity, the “red” variant, and blue light at an increased intensity, the “blue” variant) on the parameters of photosynthetic dark and light reactions, respiration rate, leaf reflectance indices, and biomass, among other factors in lettuce (Lactuca sativa L.). The same light intensity (about 180 µmol m−2s−1) was used in both variants. It was shown that the blue illumination variant increased the dark respiration rate (35–130%) and cyclic electron flow around photosystem I (18–26% at the maximal intensity of the actinic light) in comparison to the red variant; the effects were dependent on the duration of cultivation. In contrast, the blue variant decreased the rate of the photosynthetic linear electron flow (13–26%) and various plant growth parameters, such as final biomass (about 40%). Some reflectance indices (e.g., the Zarco-Tejada and Miller Index, an index that is related to the core sizes and light-harvesting complex of photosystem I), were also strongly dependent on the illumination variant. Thus, our results show that the red illumination variant contributes a great deal to lettuce growth; in contrast, the blue variant contributes to stress changes, including the activation of cyclic electron flow around photosystem I.