Growth of Pelargonium sidoides DC. in response to water and nitrogen level

Water stress is the most limiting factor in agricultural productivity in arid and semi-arid regions and causes very high losses in crop yield. Regulation of growth and stomatal conductance are the main mechanisms by which plants respond to water stress. Pelargonium sidoides is a medicinal plant that grows in South Africa and is used for the treatment of upper respiratory ailments. Cultivation has been considered as a viable means of reducing the pressure on natural populations of this species, but little to no information is available in this regard. Water and nitrogen supply are two of the most important factors that affect growth and yield of plants. This study therefore aimed at investigating the physiological and morphological response, in relation to growth, of P. sidoides to soil water and nitrogen levels. To achieve this objective, P. sidoides plants were grown under a rainshelter and exposed to three irrigation levels (well watered control, moderate water stress, and severe water stress treatment) and four nitrogen levels (0, 50, 100, and 150 kg · N · ha− 1). Nitrogen and water level had no significant interaction effect on measured parameters. Water stress significantly reduced stomatal conductance, while nitrogen had no significant effect on it. The well watered control had a significantly higher leaf area index, plant height, leaf area, and fresh root yield compared to the water stressed treatments. Nitrogen level had a significant effect on number of leaves, where 100 kg · N · ha− 1 had a significantly higher number of leaves compared to other nitrogen treatments. The study provides a first report on the response of P. sidoides to water and nitrogen and showed that the plant responds to water stress by closing its stomata and employing other morphological strategies like reducing plant growth.