硅素分期施用对镉污染水稻光合特性及物质积累的影响

硅(Si)可有效提高水稻对镉(Cd)的抗性，但关于优化硅肥管理对水稻耐Cd性、光合及物质积累等响应机制尚不明晰。采用受污染的农田土壤，通过盆栽试验研究移栽期施Si(T)、拔节期施Si(J)、移栽和拔节期等量分期施Si(TJ)对Cd污染水稻光合作用及物质积累的影响，以不施Si(CK)为对照。结果表明：施Si可明显提高Cd污染下水稻净光合速率，延长叶片光合功能，促进叶片Si沉积，增加Cd在叶中的固定，减少其向籽粒转移。与CK相比，TJ处理在全生育期具有较高的光合速率，产量显著高于其他处理。T、TJ、J处理叶片细胞壁Cd的固持量分别增加11.45%、24.16%和30.15%,且叶片Cd更多以惰性形态(包括果胶和蛋白质结合态Cd、不溶解性磷酸Cd和残渣态Cd)存在，导致叶片Cd转移系数降低，T、TJ、J较CK分别降低33.91%、56.67%和52.16%。此外，主成分分析结果表明，3种Si处理对水稻耐Cd性和光合特性的综合影响大小为TJ>J>T。综合考虑Si调控光合作用、产量、叶片和籽粒Cd浓度的效应，推荐Si素于移栽期与拔节期分期施用。

Effects of silicon staged application on photosynthetic characteristics and matter accumulation in Cd-contaminated rice

Silicon (Si) can improve the resistance of rice to cadmium (Cd) effectively, but the response mechanisms of optimized Si fertilizer management on Cd tolerance, photosynthesis and matter accumulation of rice remain unclear. In this paper, pot experiments were conducted to study the effects of Si applied at transplanting stage (T), jointing stage (J), and split at transplanting and jointing stages (TJ) on photosynthetic characteristics and matter accumulation in rice. No Si application was used as the control (CK). The results showed that Si application effectively improved the net photosynthetic rate and extended the photosynthetic function of rice under Cd-pollution, promoted Si deposition in leaves, increased Cd immobilization in leaves, and reduced the transfer of Cd to grains. Compared with CK, the photosynthetic rate of TJ treatment was much higher in the whole growth period, and the yield of which was significantly higher than that of other treatments. The T, TJ, and J treatments increased the retention of Cd in leaf cell walls by 11.45%, 24.16%, and 30.15%, respectively, while more intracellular Cd existed in inert forms (including pectin and protein binding Cd, insoluble phosphoric acid Cd and residual Cd). Furthermore, the migration factors of Cd from leaves to grains were significantly decreased, and those of T, TJ and J were 33.91%, 56.67% and 52.16% lower than CK, respectively. In addition, principal component analysis showed that the comprehensive effect of the three Si treatments on Cd tolerance and photosynthetic characteristics of rice was expressed as TJ > J > T. Considering the effect of Si on photosynthesis, yield and Cd concentration in rice grains and leaves, it is recommended that Si application would be split at transplanting and jointing stage.