硅素分期施用对土壤镉形态和水稻镉累积的影响

Effects of split silicon application on the fractions of Cd in soil and its accumulation in rice

为了探明硅素运筹对土壤-水稻(Oryza sativa L.)体系中Cd迁移的影响,探索缓解Cd污染土壤中水稻吸收和积累Cd的最佳施硅时期和施硅比例,采用盆栽实验,以稻田土壤为供试土壤,外源添加氯化镉模拟Cd含量为100 mg·kg^(-1)的污染土壤,在施硅总量(56 mg·kg^(-1)土壤)不变的基础上设置基施硅素(C1)、基肥和拔节期硅素1∶1分期施用(C2)和拔节期施硅素(C3)3种处理,以不施硅(CK)为对照,研究硅素分期施用对土壤Cd的形态以及水稻对Cd的吸收、转运和累积的影响。结果表明:与CK相比,C2和C3处理水稻成熟期土壤中Cd含量增加19.4%(P<0.05)、18.9%(P<0.05),C2和C3土壤可交换态Cd含量降低27.3%(P<0.05)、27.1%(P<0.05),而土壤残渣态Cd含量分别增加97.7%(P<0.05)、111.3%(P<0.05)。成熟期各施硅处理水稻的根和糊粉层中Cd含量显著增加,而茎、叶和精米中Cd含量明显降低,其中C1、C2和C3精米的Cd含量分别比CK降低13.8%(P<0.05)、35.1%(P<0.05)和27.9%(P<0.05),茎、叶、精米的Cd转移系数和富集系数也显著降低,而根的Cd富集系数显著升高。此外,本研究还发现土壤各形态Cd含量与水稻根和精米中Cd累积量有着显著的相关关系。综上表明,C2和C3成熟期土壤Cd的有效性显著降低,残渣态Cd显著增加,Cd从土壤向稻株中的转移受到抑制,水稻吸收的Cd大部分累积在根部,降低Cd向地上部各器官的迁移,从而导致精米Cd含量和累积量明显降低,其中C2处理更利于整个生育期土壤可还原态Cd含量的减少和抽穗期土壤中可氧化态Cd含量的增加,利于抽穗前水稻生长发育。C2处理施硅效果好,值得推荐。

The aims of this study are to investigate the influences of silicon application on the migration of cadmium in soil-rice（Oryza sativa L.）systems and to explore the optimal timing and ratio of silicon application for alleviating the uptake and accumulation of Cd in Cdcontaminated soil. A pot experiment was carried out to study the effects of silicon application at different stages on the fractions of Cd in soil and on the uptake, transport, and accumulation of Cd in rice. Cadmium chloride was added to simulate polluted soil with a Cd content of 100 mg·kg^（-1）. Based on the same total amount of silicon application（56 mg·kg^（-1））, three kinds of silicon application methods were designed：silicon applied as basal fertilizer（C1）, silicon applied as basal fertilizer and at jointing stages with a ratio of 1∶1（C2）, and silicon applied at jointing stages（C3）. No silicon application was used as the control（CK）. The results showed the Cd contents in soil at the mature stage increased by 19.4%（P〈0.05）and 18.9%（P〈0.05）with the C2 and C3 treatments, respectively, compared to the CK levels. The exchangeable Cd contents in soil with C2 and C3 treatments decreased by 27.3%（P〈0.05）and 27.1%（P〈0.05）, respectively, whereas the residual Cd contents in soil increased by 97.7%（P〈0.05）and 111.3%（P〈0.05）, respectively. The Cd contents in roots and the aleurone layer treated with silicon at maturity were elevated significantly, whereas those in stems, leaves, and white polished rice were lower. Furthermore, the Cd contents in the white rice were lower by 13.8%（P〈0.05）, 35.1%（P〈0.05）, and 27.9%（P〈0.05）with C1, C2, and C3 treatments, respectively, compared to the CK levels. The transfer factors and bioconcentration enrichment factor（BEF）of Cd in stems, leaves, and polished rice at the mature stage were reduced by silicon application. However, the BEF of Cd in roots was increased. Furthermore, there was a significant correlation between the content of different fractions of Cd in soil and Cd accumulation in roots and polished rice. In summary,soil Cd availabilities with the C2 and C3 treatments at the mature stage were reduced, whereas residual Cd were significantly increased with silicon application. The transfer of Cd from the soil to the rice plant was inhibited, and much of the Cd absorbed by the rice was deposited in roots, which reduced the migration of Cd to aboveground. Consequently, the content and accumulation of Cd in white rice were decreased explicitly and those in polished rice were significantly decreased. In addition, C2 treatment was more effective for reducing the content of reducible Cd in soil throughout the growth period, increased the content of oxidizable Cd in soil at the heading stage, and promoted the growth and development of rice before the heading stage. The effect of C2 treatment was the best, and thus was recommended for practical use.