Elevated CO2 and temperature effect on growth, phenology, biomass and hypericin content of Hypericum perforatum L. in the western Himalaya

Hypericum perforatum L. is a medicinal plant used in traditional and modern medicines in treating neurological disorders and depression. Still, there is a shortage of information on elevated CO2 (eCO2) and elevated temperature (eT) effect on this plant. Therefore, an experiment was conducted at ambient CO2 (390 µmol mol−1), elevated CO2 under free air CO2 enrichment (FACE, 550 ± 50 µmol mol−1) and elevated temperature under free air temperature increase (FATI, 2.5 ± 0.5 °C above ambient) facilities at Palampur, India during 2013–2014 and 2014–2015. During both the years, the number of branches, dry biomass (leaf, root, and flower), aboveground biomass increased under eCO2 over ambient. Averaged across both the year, total dry biomass increased by 10.4% in eCO2 at 6 months after exposure (MAE). However, by 12.6% at 8 MAE compared to ambient, decreased by 7.3% under eT at 6 MAE, respectively. Hypericin concentration was significantly higher under eT over ambient at 6 MAE. Phenological stages were advanced considerably by 3.0 to 3.5 days under eT as compared to ambient conditions. Vermicompost application increased leaf, stem and root dry biomass compared to control at 8 MAE during both the years. The results suggested that eCO2 stimulated plant biomass production and eT decreased biomass, advanced phenological stages, and enhanced hypericin content compared to ambient conditions.