硒对菜地土壤镉微区分布及其吸附解吸特性的影响

以南方酸性黄棕壤为研究对象,采用根箱进行小白菜种植,研究了不同剂量的外源硒(0、0.25、1.00 mg·kg-1,以Se计)处理下,小白菜根际与非根际土壤Cd的含量变化;同时,通过Langmuir和Freundlich吸附模型进一步分析了经Se(0、0.25、1.00 mg·kg-1)预处理并经历过小白菜生长的根际与非根际土壤对Cd的吸附与解吸特性.结果表明,在Cd含量较低(0.50 mg·kg-1)的土壤中,低剂量的Se处理(0.25 mg·kg-1)根际土壤与非根际土壤的Cd含量均高于Se剂量为0、1.00 mg·kg-1的两个处理;在Cd含量较高(5.00 mg·kg-1)的土壤中,不同剂量的Se处理未能对土壤中Cd含量造成显著差异.通过吸附解吸试验及Langmuir和Freundlich两种吸附模型的模拟,发现根际土壤对Cd的吸附容量和吸附能力均小于非根际土壤,且根际土壤Cd的非专性吸附比率大于非根际土壤,表明小白菜的生长能够改变根际土壤对重金属Cd的吸附解吸特性,增加土壤中Cd的环境风险;然而,在本实验剂量范围内,外源Se预处理并未显著改变小白菜土壤Cd的吸附解吸特性,尚不足以证明Se通过影响小白菜根系分泌物等微域环境进而改变土壤重金属Cd的吸附解吸等环境化学行为.

Effects of selenium on cadmium distribution and adsorption/desorption in rhizosphere soils of vegetable field

The experimental soil is acid yellow brown soil, and this study investigated the change of Cd content in rhizosphere and non-rhizosphere soil by pre-treating Chinese cabbage cultivated in a rhizobox system with different contents (0, 0.25, 1.00 mg·kg^-1) of exogenous selenium. Moreover, the adsorption / desorption characteristics of cadmium in the rhizosphere and non-rhizosphere soil was analyzed through Langmuir and Freundlich adsorption model. The results showed that in soil with 0.50 mg·kg^-1 Cd, the rhizosphere and non-rhizosphere soil pre-treated with 0.25 mg·kg^-1 Se had higher content of Cd than those pre-treated with 0 and 1.00 mg·kg^-1 Se. In soil with 5.00 mg·kg^-1 Cd, the content of Cd was nearly independent on Se pre-treatments. In addition, the results of Langmuir and Freundlich models showed that the adsorption capacity of rhizosphere soil was less than the non-rhizosphere soil, and the non-specific desorption ratio of rhizosphere soil was higher than that in the non-rhizosphere soil, indicating that the Chinese cabbage's growth could change the adsorption and desorption characteristics of rhizosphere soil, thus increasing the environmental risk of Cd in soil. However, this study found no significant difference in the adsorption and desorption in rhizosphere and non-rhizosphere soil with different Se pre-treatments. Furthermore, our findings were not sufficient to conclude that selenium changed the environmental behaviors of Cd in soil by regulating the characteristics of root exudates.