Genotype-dependent growth and essential oil responses of Salvia officinalis under combined elevated CO2 and heat stress

Global climate change involves simultaneous increases in atmospheric CO 2 concentration and temperature, imposing complex constraints on plant performance. This study examined the interactive effects of elevated CO 2 (400–1000 ppm) and temperature (26/16, 29/19, and 32/22 °C day/night) on growth, essential oil yield, and chemical composition of four Salvia officinalis genotypes. A significant CO 2 × temperature × genotype interaction was detected for growth parameters ( P < 0.05) and essential oil ratio ( P < 0.05), revealing that CO 2 induced growth stimulation was strongly modulated by thermal conditions. Elevated CO 2 enhanced biomass and oil yield under moderate temperatures, whereas heat stress (32/22 °C) markedly constrained this fertilization effect, particularly in the thermosensitive genotype A1. In contrast, genotypes A3 and A4 maintained relatively stable biomass and metabolite production, indicating superior phenotypic plasticity and metabolic buffering capacity. Climate stress also induced substantial shifts in essential oil composition, with oxygenated monoterpenes showing pronounced genotype-dependent sensitivity to temperature × CO 2 interactions. Multivariate analyses confirmed that temperature was the primary driver of chemical divergence, while genotype determined overall chemotype stability. These findings suggest that genotype-specific differences in growth stability and chemical composition under combined CO 2 and heat stress reflect differential capacity for physiological adaptation, highlighting genotype selection as a key strategy for sustaining both productivity and phytochemical integrity under future warming scenarios.