Foliar application of selenium increased selenium accumulation, speciation, and bioaccessibility, as well as the yield and nutritional quality of sweet maize

Introduction Selenium (Se) deficiency remains a significant global nutritional issue, emphasizing the need for efficient crop-based biofortification interventions. Methods This study examined the mechanistic responses of sweet maize ( Zea mays L .) to foliar Se fertilization (0, 20, 40, and 60 g ha −1 ), focusing on antioxidant regulation, physiological traits, nutrient metabolism, Se speciation, and Se bioaccessibility. Results Moderate Se doses (20–40 g ha −1 ) enhanced chlorophyll retention and photosynthetic efficiency, accompanied by increased activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as 22.8% reduction in malondialdehyde (MDA), indicating improved redox homeostasis. These biochemical improvements facilitated higher assimilate accumulation, resulting in a 2–7% increase in fresh cob yield and enhanced levels of soluble sugars, amylose, protein, vitamin C, and key micronutrients (magnesium, iron, copper, manganese). However, excessive Se (60 g ha −1 ) caused oxidative imbalance, leading to decreased enzyme activity and reduced yield. Kernel Se concentration increased significantly with Se supply, dominated by selenomethionine (SeMet) (82.3% of total Se), exhibiting high in vitro bioaccessibility (35.6% gastric, 76.0% intestinal). Discussion The coordinated regulation of antioxidant defense and nutrient metabolism under optimal Se supply enhances both plant physiological performance and the nutritional bioefficacy of edible kernels, providing a mechanistic framework for sustainable Se biofortification.