Moisture stress and nitrogen availability modulate the secondary metabolite profiles, enzymatic activity, and physiological and agronomic traits of Stevia rebaudiana

Abstract

Performances of crops are mainly influenced by frost, heat and availability of soil-water and nitrogen (N). However, little is known about the interaction between soil-water and N on Stevia rebaudiana. Thus, a field experiment was conducted with fifteen treatment combinations comprising three levels of soil-moisture (irrigation at 20, 50 and 75 kPa soil-water-potential) and five N levels (0–140 kg ha−1) to understand how soil-moisture and N influence growth, physiological and biochemical activities of stevia. Plants irrigated at 50 kPa registered 6.3–18.9% and 20.7–21.2% higher dry leaf yield compared with 20 and 75 kPa, respectively. No significant (P ≥ 0.05) differences in concentrations of total steviol glycosides (TSGs) in leaf were found due to moisture regimes. Total soluble sugars (TSS), proline, total phenols were decreased significantly (P ≤ 0.05) with plants irrigated at 20 kPa whereas SOD, CAT, and POX were decreased at both excessive and deficit water conditions. Photosynthetic rate (PN) and stomatal conductance (gs) decreased with plant irrigated at 75 kPa. Anatomical changes in leaf were also observed due to different moisture regimes. Among the N levels, 105 kg ha−1 registered approximately 50–53% higher dry leaf yield compared with control (0 kg N ha−1), irrespective of irrigation level. Excess (140 kg ha−1) and shortage of N significantly decreased the PN, gs, and enzyme activities. Concentrations of TSS and TSGs were higher with N at 105 and 70 kg ha−1, respectively. Our results emphasize that irrigation at 50 kPa and application of N 105 kg ha−1 is the suitable combination for sustainable cultivation of stevia.