Responses of differential nitrogen doses on biomass, biochemical, and medicinally important metabolites of Andrographis paniculata exposed to elevated level of carbon dioxide

In this study, the effects of different levels of nitrogen (N) and elevated CO₂ (ECO₂) were evaluated using open-top chambers (OTCs) on the carbon and nitrogen pool, medicinally important metabolites, biomass accumulation, and the biochemical parameters of an important medicinal plant, Andrographis paniculata. In the present study, ECO₂ increased the protein and chlorophyll contents at higher N level compared with low N availability. The level of reactive oxygen species decreased with increased N supply under ECO₂ however, responses of enzymatic antioxidants to ECO₂ at various N treatments showed variable responses. All N treatments resulted in higher organic carbon content due to ECO₂. However, a reduction in N content at low and moderate doses of N treatment was observed leading to an increased carbon-to-nitrogen (C/N) ratio under ECO₂. At higher N treatments, biomass allocation to the root, stem, and leaf was considerably higher under ECO₂. Furthermore, ECO₂ increased the total alkaloid content at all N levels; however, the increase was highest at recommended level of N. Further, there were differences in responses of two active medicinally important metabolites of the plant. Though ECO₂ increased andrographolide and neo-andrographolide content at N supplementation, but the increment in andrographolide was highest at recommended dose of N. The results of the study indicated that under ECO₂, biomass gain is benefitted at high N supply, while medicinally important metabolites were found more at moderate level of N.