Climate-induced changes in essential oil production and terpene composition in alpine aromatic plants

•Three years of CO2 enrichment and warming experiment was conducted on alpine aromatic herbs.•Plant essential oil yield and monoterpenes decreased in warmer and CO2 enriched environment.•The ratio of oxygenated to non-oxygenated terpenes decreased may affect the therapeutic properties of the essential oil. Alpine regions are biodiversity hotspots for endemic species with unique adaptations to harsh climatic conditions. These adaptations often involve specialized behaviours and metabolism including the production of secondary metabolites that protects plants from environmental stresses. This study examines the impacts of elevated CO2 (eCO2) and combined effects of elevated CO2 and temperature (eCO2+T) on two alpine aromatic herbs, namely Angelica glauca and Nardostachys jatamansi. These species were raised in open-top chambers (OTCs) and treated with elevated CO2 (600 ppm) and temperature (+2.0 °C from control) during 2018 to 2020. The primary (total soluble sugar, starch, total soluble protein, amino acid and proline contents), secondary metabolites (Phenolics, essential oil yield, and components using GC-MS) and antioxidant activities (superoxide dismutase and peroxidase) were measured. Total soluble sugar increased under eCO2, while starch content, total amino acid and total soluble protein initially increased but later declined in response to the treatments. Proline content and antioxidant activities were higher under eCO2 and eCO2+T treatments. Total phenolic content showed both increasing (in A. glauca) and decreasing (in N. jatamansi) responses to eCO2 and eCO2+T treatments. GC–MS analysis showed decreased monoterpenes in CO2 and temperature treatments, but some sesquiterpenes showed mixed responses with both increases and decreases. These findings suggest that changes in climate can alter the composition of secondary metabolites in alpine herbs, potentially affecting their therapeutic properties and suitability for use in herbal medicine. This study provides valuable insights into the species-specific physiological responses of plants to changing climate.