多金属硫化物矿区水稻根际土壤中重金属形态的迁移转化

选取酸性矿山废水污灌形成的多重金属污染水稻土,采用多格层根际箱模拟水稻根际环境,运用BCR连续提取法研究水稻生育中后期的4个不同时期(分蘖期、孕穗期、扬花期、乳熟期)中根际土壤中重金属Cd、Cu、Pb和Zn的形态分布和迁移转化特征。结果表明,在4个时期中Cu、Pb和Zn均以生物有效性较低的形态为主,未发现Cu、Pb和Zn在各土层明显的迁移转化,在根际S0层Cu总量略有增加,Pb和Zn略有降低。这3种元素的弱酸提取态也在根际S0层有所增加,但变化不显著;而弱酸提取态Cd明显在根际土壤中富集,其在S0层的含量约为其他土层的3倍。此外,研究结果还指出,随着生育期的延长Cd含量在不同土层都呈现出先增加后降低再增加的变化趋势,而Cu、Pb和Zn的变化不明显。研究表明,在水稻生育中后期根系仍然能影响根际中金属形态的变化和迁移能力,但对Cd比对Cu、Pb和Zn的影响更大;并且在生育期的中后期水稻对Cu、Pb和Zn几乎不再吸收,但对Cd的吸收能力依然很强。

Effect of Rhizospheric Environment of Rice on Bioavailability and Mobility of Cd, Cu, Pb and Zn in AMD Polluted Paddy Soil

The effects of root system of rice plants on the fractionation of cadmium, copper, lead and zinc were investigated using rhizobox system from tillering to milk ripe state. The soil samples were taken from the multimetal-contaminated paddy soils due to the irrigation of acid mine drainage for more than 40 years. BCR method was used to evaluate the forms and mobilization of heavy metals in the rhizosphere soil. The results showed that copper, lead and zinc were dominated mainly by the form of lower bioavailability and their mobility was not observed different obviously from non-rhizospheric soil to the rhizosphere soil. Howerver, there was a significant change in the forms of cadmium. The acetic acid extractable Cd in the root compartment was 3 times higher than that in the other compartments. Cd content in different soil layers showed an initial increase and then a decrease and a final increase pattern with the growth stages. Furthermore, it showed that, unlike Cu, Pb and Zn, Cd concentration in root compartment decreased significantly at the milk ripe stage indicating a rapid uptake of Cd in the later growth stage.