Soil microplastic pollution may affect woody plant establishment, but evidence for tree seedlings remains limited. Populus simonii × P. nigra ‘1307’ seedlings were grown for 45 d in soil containing an equal-mass PVC–PE–PS mixture at 0, 100, 500, or 1000 mg kg⁻¹ dry soil. Growth, root architecture and activity, photosynthetic traits, oxidative status, and soil chemical and enzymatic properties were measured. The 100 mg kg⁻¹ treatment produced limited, trait-specific changes and did not consistently inhibit growth. In contrast, 500 and 1000 mg kg⁻¹ reduced most growth and physiological traits. At 1000 mg kg⁻¹, total dry biomass, total root length, root surface area, root volume, root-tip number, and root activity decreased by 43.7%, 46.5%, 47.2%, 50.2%, 51.1%, and 50.9%, respectively. Net photosynthetic rate and PSII electron transport declined, whereas H₂O₂, O₂•⁻ production, thiobarbituric acid-reactive substances (TBARS), and electrolyte leakage increased. Under higher exposure, soil electrical conductivity was higher, whereas available nutrient levels and several soil enzyme activities were lower. These results indicate that medium and high concentrations of the tested mixture were associated with concurrent inhibition of root development, photosynthetic performance, and biomass accumulation under short-term pot conditions. Because concurrent impairment of woody-seedling performance and soil biochemical functioning may compromise vegetation establishment, these findings support the inclusion of mixed-polymer exposure in ecological risk assessments for soils used in forestry and ecological restoration.

Salt stress restricts cucumber seedling establishment by impairing root development, photosynthesis, ion homeostasis, and redox balance. This study examined whether potassium silicate (K₂SiO₃) could partially alleviate these responses under hydroponic sodium chloride (NaCl) stress. Cucumber seedlings were exposed to six treatments: a nutrient-solution control, K₂SiO₃ alone supplying 1.0 mmol L⁻¹ silicon (Si), 75 mmol L⁻¹ NaCl, and NaCl combined with K₂SiO₃ supplying 0.5, 1.0, or 2.0 mmol L⁻¹ Si. Growth, root morphology, photosynthetic pigments, gas exchange, chlorophyll fluorescence, photosystem II (PSII) energy partitioning, oxidative injury, antioxidant enzyme activities, osmotic adjustment, and ion status were evaluated at 7 and 14 d. NaCl markedly reduced seedling growth, root development, net photosynthetic rate, PSII photochemical performance, and electron transport, while increasing leaf sodium (Na⁺), malondialdehyde accumulation, non-photochemical quenching, non-regulated energy loss, proline, and soluble sugar. K₂SiO₃ partially alleviated these changes. The treatment supplying 1.0 mmol L⁻¹ Si produced the strongest integrated recovery of growth, root activity, photosynthetic performance, PSII function, and oxidative status. The treatment supplying 2.0 mmol L⁻¹ Si resulted in the lowest leaf Na⁺ concentration and the highest leaf potassium (K⁺)/Na⁺ ratio among salt-stressed seedlings but did not produce the greatest growth recovery. These findings suggest coordinated changes in photosynthesis, photochemical energy use, redox status, and ion balance. Because K₂SiO₃ supplied both Si and K⁺, the results represent responses to K₂SiO₃ supplementation rather than Si-specific effects.