Exogenous Salicylic Acid Improves Storage Root Yield of Drought‐Stressed Sweet Potato via Enhancing Antioxidant Efficiency

ABSTRACT

Although exogenous salicylic acid (SA) has the potential to assist sweet potatoes in coping with drought stress (DS), the specific effects on leaf antioxidant metabolism and storage root yield during the bulking stage remain poorly understood. To investigate this, a pond experiment was conducted in 2024 and 2025 to assess the influences of SA on leaf oxidative damage, antioxidant systems, and final yield under DS. Results demonstrated that DS significantly elevated peroxidase, superoxide dismutase, and catalase activities in leaves. However, this increase was insufficient to regulate reactive oxygen species (ROS) levels, leading to a marked hydrogen peroxide and superoxide anion accumulation, which subsequently induced oxidative stress. Consequently, this oxidative stress significantly increased malondialdehyde (MDA) content while reducing leaf relative water content (LRWC), ultimately leading to a decrease in storage root yield by 49.26% to 55.47%. Notably, exogenous SA application reduced the total leaf antioxidant capacity and decreased peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities. Concurrently, SA treatment improved LRWC, restored chloroplast ultrastructure, and reduced abscisic acid (ABA) accumulation, thereby effectively alleviating the build‐up of ROS and MDA. Further analysis indicated that SA decreased ascorbate content and ascorbate peroxidase activity, while simultaneously increasing glutathione content and glutathione peroxidase (GPX) expression within the ascorbate–glutathione cycle. This indicates a strategic reallocation of resources towards the GSH‐GPX branch. Such an approach facilitated effective ROS scavenging at a reduced metabolic cost, thereby sustaining leaf photosynthetic capacity and enhancing final yield by 53.18% to 68.02% relative to DS alone. In conclusion, exogenous SA enhances drought tolerance in sweet potatoes not merely by elevating total antioxidant capacity, but by improving antioxidant efficiency through the restoration of leaf water status and chloroplast integrity, attenuation of ABA signalling, and resource reallocation within the AsA‐GSH cycle.