Growth Light Quality Influences Leaf Surface Temperature by Regulating the Rate of Non-Photochemical Quenching...

Significant efforts have been made to optimise spectrum quality in indoor farming to maximise artificial light utilisation and reduce water loss. For such an improvement, green (G) light supplementation to a red-blue (RB) background was successfully employed in our previous studies to restrict both non-photochemical quenching (NPQ) and stomatal conductance (g_s). At the same time, however, the downregulation of NPQ and g_s had the opposite influence on leaf temperature (T_leaf). Thus, to determine which factor plays the most prominent role in T_leaf regulation and whether such a response is temporal or permanent, we investigated the correlation between NPQ and g_s and, subsequently, T_leaf. To this end, we analysed tomato plants (Solanum lycopersicum L. cv. Malinowy Ozarowski) grown solely under monochromatic LED lamps (435, 520, or 662 nm; 80 µmol m^-2 s^-1) or a mixed RGB spectrum (1:1:1; 180 µmol m^-2 s^-1) and simultaneously measured g_s and T_leaf with an infrared gas analyser and a thermocouple or an infrared thermal camera (FLIR) during thermal imaging analyses. The results showed that growth light quality significantly modifies T_leaf and that such a response is not temporal. Furthermore, we found that the actual adaxial leaf surface temperature of plants is more closely related to NPQ amplitude, while the temperature of the abaxial surface corresponds to g_s.