Mulberry leaves are used as functional food materials, but drought can reduce leaf production and physiological stability. This study evaluated whether foliar sodium selenite application could partially alleviate drought injury while increasing total selenium and selected functional-quality indicators in mulberry (Morus alba L.) leaves. Seedlings were assigned to four treatments: normal water supply with the surfactant-containing control spray (CK), normal water supply with sodium selenite application (Se), drought stress with the control spray (D+CK), and drought stress with sodium selenite application (D+Se). Drought reduced plant growth, leaf water status, leaf pigment status, gas exchange, and PSII photochemical performance while increasing oxidative damage and membrane injury. Under drought stress, sodium selenite application partially maintained growth, water status, photosynthetic performance, and antioxidant enzyme activities and was associated with lower oxidative-damage indicators. Drought alone increased several stress-responsive secondary metabolites but reduced biomass, polysaccharides, and soluble protein, indicating a trade-off rather than a uniform improvement in leaf quality. Compared with D+CK, D+Se increased total selenium, several functional compounds, and in vitro antioxidant capacity. Overall, foliar application of 10 μM sodium selenite was associated with partial drought-stress alleviation and higher functional-quality indicators under controlled pot conditions. Further studies are required to optimize the application dose and evaluate selenium speciation, bioaccessibility, intake safety, and field performance.

High temperature can impair leaf water status, photosynthetic function, and membrane stability in ornamental woody seedlings. However, integrated evidence combining gas exchange, chlorophyll fluorescence, oxidative injury, antioxidant activity, and osmotic-adjustment-related responses in heat-stressed Syringa oblata remains limited. One-year-old seedlings from a single nursery batch were exposed for 7 d to 25/18 °C or 40/30 °C day/night conditions and sprayed with either a solvent solution or 0.5 mM salicylic acid. Growth, leaf water status, photosynthetic pigments, gas exchange, pulse-amplitude-modulated fluorescence, OJIP/JIP-test parameters, oxidative-injury markers, antioxidant enzyme activities, and osmotic-adjustment-related compounds were evaluated. Heat treatment reduced leaf relative water content, photosynthetic performance, and photosystem II function and increased reactive oxygen species accumulation, lipid peroxidation, and electrolyte leakage. Compared with heat treatment alone, seedlings receiving salicylic acid under heat showed an 82.2% higher net photosynthetic rate, a 12.2% higher maximum quantum efficiency of photosystem II, and a 116.4% higher performance index on an absorption basis. Hydrogen peroxide, malondialdehyde, and electrolyte leakage were 35.1%, 35.8%, and 32.5% lower, respectively. Antioxidant enzyme activities were also higher under heat plus salicylic acid than under heat alone, whereas additional increases in proline and soluble sugars were not statistically confirmed; soluble protein was partially maintained. Gas exchange was measured after treatment at a common leaf-chamber temperature of 25 °C and therefore represented retained photosynthetic capacity under standardized conditions. Overall, foliar application of 0.5 mM salicylic acid was associated with partial maintenance of photosynthetic function and lower oxidative injury during short-term heat exposure. Because one chamber was assigned to each treatment combination in a single experimental run, possible chamber-specific effects could not be statistically separated from treatment-related differences. Independent validation is therefore required.