Preharvest temperature treatments influence physiological traits, secondary metabolites, and volatile compounds in...

Temperature is a major environmental factor influencing plant growth, physiological performance, and secondary metabolite biosynthesis in medicinal plants. This study investigated the effects of low (18 °C), control (25 °C), and high (32 °C) temperature treatments on the growth, physiological responses, antioxidant activity, photosynthetic pigments, and volatile compound profiles of red holy basil (Ocimum tenuiflorum L.) grown under controlled environment conditions. Plants were evaluated at 3, 6, 9, and 12 days after treatment (DAT). Temperature significantly affected plant morphology, biomass accumulation, gas exchange parameters, secondary metabolites, and volatile compounds. Low temperature promoted stem elongation and markedly enhanced total phenolic, flavonoid, anthocyanin, and DPPH radical scavenging activity, with the highest total phenolic content at 9 DAT. In contrast, the control temperature resulted in the greatest shoot biomass accumulation and continuous increases in the contents of linalool and eugenol. High temperature enhanced photosynthetic rate, stomatal conductance, transpiration rate, SPAD, and NDVI values during the early treatment stages, while increasing β-caryophyllene and α-humulene accumulation at later stages. Heatmap and principal component analyses revealed distinct clustering patterns associated with temperature and treatment duration. These findings provide valuable insights into precision temperature management under controlled environment agriculture for optimizing biomass production and enhancing the accumulation of high-value bioactive compounds in red holy basil for pharmaceutical, food, and cosmeceutical applications.