Daily Short-Term Temperature Drops Can Alleviate the Negative Effect of Continuous Lighting on the Photosynthetic Apparatus in Plants

Several crops (tomato, eggplant, sweet pepper, and cucumber) were used to examine the impact of continuous (24 h a day) lighting on photosynthetic characteristics of plants grown permanently at 26°C and those exposed daily to short-term (2 h) cooling at 10°C (temperature-drop treatments). The plant response was assessed by indices characterizing the pigment complex and the photosynthetic activity of leaves. Growing plans under continuous light at a constant temperature resulted in leaf photodamage and photoinhibition in all four species, although to varying degrees. The temperature-drop treatments prevented the photodamage of leaves under continuous light in all species and enabled high sustainable levels of photosynthetic activity in tomato, pepper, and cucumber. The results suggest that temperature-drop treatments can be regarded as an agricultural technique that exploits the benefits of continuous lighting while mitigating the negative effects of constant light. However, the effectiveness of this technique would depend on the choice of optimal intensities and durations of the drop treatment since these parameters may vary depending on plant species.