Many studies have discussed the influence of elevated carbon dioxide (eCO) on modeling and crop plants. However, much less effort has been dedicated to herbal plants. In this study, a robust monitoring for the levels of 94 primary and secondary metabolites and minerals in two medicinal herbs, basil (Ocimum basilicum L.) and peppermint (Mentha piperita L.), grwon under both ambient (aCO, 360 ppm) and eCO (620 ppm) was performed. We also assessed how the changes in herbal tissue chemistry affected their biological activity. Elevated CO significantly increased herbal biomass, improved the rates of photosynthesis and dark respiration, and altered the tissue chemistry. Principal Component Analysis of the full data set revealed that eCO induced a global change in the metabolomes of the two plants. Moreover, Hierarchical Clustering Analyses showed quantitative differences in the metabolic profiles of the two plants and in their responsiveness to eCO. Out of 94 metabolites, 38 and 31 significantly increased in basil and peppermint, respectively, as affected by eCO. Regardless of the plant species, the levels of non-structural carbohydrates, fumarate, glutamine, glutathione, ascorbate, phylloquinone (vitamin K1), anthocyanins and a majority of flavonoids and minerals were significantly improved by eCO. However, some metabolites tended to show species specificity. Interestingly, eCO caused enhancement in antioxidant, antiprotozoal, anti-bacterial and anticancer (against urinary bladder carcinoma; T24P) activities in both plants, which was consequent with improvement in the levels of antioxidant metabolites such as glutathione, ascorbate and flavonoids. Therefore, this study suggests that the metabolic changes triggered by eCO in the target herbal plants improved their biological activities.

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The functional food value of herbal plants is greatly related to their contents of valuable phytochemicals. Regarding its impact on primary and secondary plant metabolism, CO enrichment could be a candidate strategy to modulate the levels of nutritionally and medicinally interesting phytochemicals in herbal plants. Herein, the concentrations of 81 metabolites and minerals were evaluated in shoot tissues of parsley and dill grown under two levels of CO, ambient (378 ± 25 µmole CO mole air, aCO) and elevated (627 ± 24 µmole CO mole air, eCO). Regardless of the plant species, eCO improved the levels of soluble sugars, starch, organic acids, some EAAs, most of USFA, total phenolics, total flavonoids and vitamins A and E. However, notable variations in the metabolites responsiveness to eCO were recorded among the tested plant species. Moreover, considerable improvements in the total antioxidant capacity, antiprotozoal, antibacterial and anticancer activities were recorded for parsley and dill in response to eCO.