The responses of Spartina alterniflora Loisel. roots to the interactive effects of drought and nitrogen (N) form, and the underlying mechanisms involved, remain poorly understood. We conducted a greenhouse experiment to evaluate the effects of N form (NH4 +, NO3 -, and NO3 -/NH4 +) and increasing water deficit on root performance, including growth, metabolite profiles, antioxidant activity, and N metabolism. Under well-watered conditions, NH4 +-fed plants exhibited the greatest root growth, nearly double that of NO3 --fed plants. However, this growth advantage was lost under mild (50% field capacity, FC) and severe (25% FC) drought stress. In contrast, drought stress enhanced root growth in NO3 --fed plants relative to well-watered conditions. Under well-watered conditions, NH4 + nutrition increased the activities of superoxide dismutase, glutathione reductase, and ascorbate peroxidase compared to NO3 - nutrition. Although drought stress further stimulated antioxidant enzyme activities in the roots of NH4 +-fed plants, this response did not mitigate drought-induced growth reductions. Antioxidant enzyme activities in the NO3 -- and NO3 -/NH4 +-fed plants were largely unaffected by drought, except for guaiacol peroxidase. Regardless of N form, glutamine synthetase activity increased under mild drought stress but declined under severe stress. Drought stress also enhanced glutamate dehydrogenase activity across all N treatments, particularly in NH4 +-fed plants, and was accompanied by increased total amino acid concentrations, especially proline. Despite these metabolic adjustments, drought stress reduced the overall performance of NH4 +-fed plants. These findings provide insights into N form-dependent drought responses and may help guide fertilizer management strategies to improve S. alterniflora productivity under water-limited conditions.
Jeddi et al. (2026) studied this question.