Objective  The aims were to explore the effects of Silicon (Si) application on growth, photosynthesis and antioxidant system of rice under Cadmium (Cd) stress in northern paddy soil, so as to provide a theoretical basis for further application of Si to alleviate Cd toxicity in rice.

  Method  Under different Cd addition levels (0, 1, 3 and 5 mg kg⁻¹), the effects of different Si concentrations (0, 100, 300 and 500 mg kg⁻¹) on rice growth, leaf photosynthesis and antioxidant system in the pre- fertility period (to tillering stage) were studied by using the pot experiment.

  Result   The rice plant height, root length and biomass (aboveground and root fresh weight), chlorophyll content, net photosynthetic rate (Pn), intercellular CO₂ (Ci) and transpiration rate (Tr) in rice leaves were decreased significantly under different Cd concentrations, and the Cd content in rice shoot was increased. When the amounts of Cd applied were 3 and 5 mg kg⁻¹, stomatal conductance (Gs) decreased significantly in rice leaves. Under Cd stress, Si application increased chlorophyll content and photosynthetic characteristics of rice leaves, decreased Cd content in rice shoot. The plant height, root length and biomass of rice were also increased with the application of Si. For the antioxidant system, compared with the blank control (Si0Cd0), when 3 and 5 mg kg⁻¹ Cd was applied, SOD and CAT activities were significantly decreased by 16.9%, 26.3% and 9.3%, 15.7%, while POD activities were significantly increased by 51.1% and 66.6%. MDA and Pro contents significantly increased in rice leaves under Cd stress. Compared with no Si application, under different concentrations of Cd stress, the SOD and CAT activities of rice leaves were significantly increased by 20.4%-58.9%, 25.3%-72.5% and 5.8%-11.9%, 22.7%-25.4% in 100 and 300 mg kg⁻¹ Si treatment respectively. POD activities decreased significantly by 21.2%-43.0% and 31.8%-50.8%. At the same time, 300 and 500 mg kg⁻¹ Si significantly reduced MDA and Pro contents in rice leaves.

  Conclusion  different supplemental levels of Si had appreciably improved on growth, leaf chlorophyll content, photosynthetic characteristics and antioxidant system of rice in the pre- fertility period under Cd stress, and the effect of 300 mg kg⁻¹ Si treatment was the best.