Effect of the Spectral Composition of LED Artificial Lighting Sources on the Functional Activity of the Photosynthetic Apparatus of Basil Leaves

The influence of six experimental light sources (lamps) based on LEDs with different emission spectra simulating optical radiation close to solar radiation on the photochemical activity of photosystems (PS) of purple basil leaves and on the redox state of the P700 reaction center was studied. The spectra differed in the photon flux distribution over the main emission spectrum ranges, correlated color temperature (CCT), and general color rendering index (R_a). A comparative analysis of PAM fluorometry parameters resulted in the identification of the spectral regions that ensure more efficient photosynthetic processes in basil leaf cells at stages of technical ripening and flowering. In particular, basil plants grown on a spectrum with a CCT of 5260 K and R_a 98 had a fairly low F₀ level, one of the highest F_v/F_m ratios characteristic of plants under nonstressful conditions, one of the highest quantum yields of both PS Y(I) and Y(II), and high electron flow rates. Spectra with CCT 4550 K and R_a 91 and with CCT 2820 K and R_a 81 also looked promising in terms of PAM fluorometry parameters. The spectrum with CCT 2990 and R_a 97 had the worst performance in terms of the studied PSI and PSII parameters.