Enhancing tomato tolerance to low phosphorus stress through exogenous nano-silicon application

• Nano-silicon more effectively alleviates LP stress than ionized Si. • Nano-silicon application reduced ROS accumulation under LP stress by enhancing antioxidant defenses. • Nano-silicon application remodeled carbohydrate metabolism in both root and leaves of tomato seedlings under LP stress. • Additional nano-silicon following LP stress is a more effective measure than ionized silicon to improve tomato fruit quality during the fruiting period. Phosphorus is essential for plant growth, but excessive fertilizer may deplete phosphate rock reserves and cause environmental issues like eutrophication. Silicon has been reported to improve phosphorus use efficiency, yet the physiological and morphological responses of plants to low-phosphorus (LP) stress across developmental stages remain insufficiently characterized. In this study, we investigated the impact of ionic and nano-silicon foliar sprays (20 and 100 mg·L⁻¹) on the LP stress responses of hydroponically grown tomato seedlings. LP stress hindered seedling growth, elevated lipid peroxidation, and impaired carbohydrate metabolism, leading to altered fruit morphology and quality. Among all treatments, 100 mg·L⁻¹ nano-silicon most effectively reduced ROS accumulation through enhanced antioxidant enzyme activities. It also optimized carbohydrate metabolism by upregulating sucrose synthase and invertase activities, thereby promoting organic matter accumulation and allocation. These improvements increased tomato yield by ∼19 % under LP stress. Fruit quality was also enhanced, with soluble sugar, sucrose, and vitamin C contents increasing by ∼50 %, ∼70 %, and ∼47 %, respectively. Overall, these findings demonstrate that exogenous foliar application of nano-silicon represents a promising agronomic strategy for improving the tolerance of tomato seedlings and fruit quality under LP conditions.