Effect of nitrogen nutrition on water-deficit stress tolerance potential of Withania somnifera (L.) Dunal

It is reported that medicinal plants grown under semiarid climates are more pronounced in secondary metabolites, however, at the cost of compromised growth and yield. In the present investigation, the effectiveness of soil nitrogen application (0 and 50 kg N ha⁻¹) on growth, and secondary metabolite contents in Withania somnifera under drought stress (100% field capacity, 70% field capacity, and 50% field capacity) were assessed. Plant height, shoot biomass and total biomass were significantly decreased under drought stress. It is important to note that the moderate drought stress had not any significant effect on root biomass whereas the severe drought stress significantly decreased the root biomass. Chlorophyll pigments were also significantly decreased under drought stress. The drought-induced increase was observed in lipid peroxidation, proline content, as well as antioxidative enzyme activity. Secondary metabolite content like total phenols and flavonoids was also shown to increase under drought stress. The soil nitrogen application significantly improved the total biomass, chlorophyll pigments, and proline content under both moderate and severe drought stress. The lipid peroxidation was decreased under nitrogen application in drought-stressed plants. Superoxide dismutase and catalase activity was increased under soil nitrogen application in both moderate and severe drought stress. Whereas, the total phenol and flavonoids content increased in response to soil nitrogen application under severe drought stress. Withanolide A content was increased in response to soil nitrogen application in both control (1.67 ± 0.10 mg g⁻¹ DW) as well as in moderately stressed plants (1.58 ± 0.14 mg g⁻¹ DW). The study reveals that soil nitrogen application improved the drought stress tolerance potential of W. somnifera through enhanced levels of chlorophyll pigments, proline, and antioxidative defence system. Elicitation by both nitrogen and drought significantly enhanced the secondary metabolite content of W. somnifera.