Foliar application of selenium improves drought tolerance in tomato with temporal changes in antioxidant and osmotic responses

Drought severely constrains tomato growth and productivity. Foliar application of selenium (Se) has demonstrated capable of improving drought tolerance of horticultural crops. However, the temporal variation in Se-associated antioxidant and osmotic responses in drought-stressed tomato remains elusive. To address this, we conducted aa two-year pot experiment in 2023 and 2024 where three irrigation regimes were established by triggering irrigation whenever soil water content drops to of 50%, 65% and 80% of field capacity, which represents severe drought, moderate drought, and well-watered condition, respectively. Plant leaves were sprayed with 0, 2.5, 5, or 10 mg·L -1 of Se. Physiological traits were measured in 2023 at a single time point, at 1, 5, 10, and 15 d after Se application in 2024. The representative treatments were analyzed by untargeted metabolomics at 5 d The results show total aboveground dry matter and fruit dry matter decreased with increasing drought severity; compared with W3, W1 reduced them by 35.5% and 32.5%, respectively. At a given water regime, the strongest positive response was generally observed at Se2.5. Under W1, Se2.5 increased total aboveground dry matter and fruit dry matter by 33.6% and 42.1%, respectively, and at 10 d after Se application reduced H 2 O 2 and MDA contents by 20.9% and 20.7% relative to Se0. In contrast, Se10 was associated with higher oxidative stress indicators and weaker growth responses than Se2.5. Time-course analysis indicated sampling-time-dependent treatment patterns: Se2.5-treated plants showed higher GPX activity and proline accumulation at early sampling points, whereas several antioxidant and osmolyte-related indicators declined at later sampling times. Metabolomic profiling at 5 d further indicated that Se2.5 application under drought was accompanied by differences in putatively annotated metabolites related to glycolysis/gluconeogenesis, pyruvate metabolism, the TCA cycle, and amino acid biosynthesis. Among the tested treatments, foliar application of 2.5 mg·L -1 Se showed the most consistent drought-alleviating effect, particularly under severe drought. Overall, low-dose foliar Se was associated with improved tomato performance under drought, together with temporally variable antioxidant and osmolyte-related physiological responses and single-timepoint metabolic associations at 5 d, suggesting its potential as a supplementary strategy for water-limited greenhouse tomato production.