Evaluating spearmint’s morphological and physiological responses under different artificial lighting systems

Indoor agriculture is becoming more relevant as a result of artificial lighting, which makes it possible to increase productivity, improve quality and cultivate where natural light is insufficient. The present study was conducted by growing spearmint inside a glasshouse under light emitting diode (LED), high pressure sodium (HPS), and light emitting diode assisted infrared (LED+IR) light treatments, while the control plants were grown outside the glasshouse under natural sunlight. Morphological analyses revealed that LED supplemental light performed better in terms of plant height, number of stems per plant, and fresh weight of the produce than all other tested light treatments, whereas HPS favored increased internode spacing. The analytical determinations revealed the outperformance of LED in terms of total carotenoids, total anthocyanins, and total sugar accumulation in spearmint leaves. Plants grown under both LED and LED+IR accumulated less nitrate than plants grown under HPS. HPS treated spearmint plants also showed a reduction in the total carotenoids and total sugar levels. Moreover, no significant changes were observed in lipid peroxidation (as measured by the thiobarbituric acid reactive substances, TBARS assay) among all treatments. On the other hand, control plants showed the highest phenolic index relative to the other light treatments which provided a brief overview of the effects of the light spectrum of artificial lighting, such as LED, HPS, LED+IR, and natural sunlight on spearmint growth, oxidative stress, and secondary metabolite production.