赤泥条件下水稻根际铁膜形成及镉吸收机理研究

Effects of Red Mud on Iron Plaque Formation in Rhizosphere and Cadmium Uptake of Rice Grown in Cd-polluted Soils

为揭示赤泥条件下水稻（Oryza sativa L.）根表和根际铁膜形成及铁膜中重金属（Fe、Mn 和Cd）分布与水稻镉（Cd）吸收的潜在关系,本文采用盆栽试验,即在2 和5 mg·kg^-1 两种镉浓度条件下,试验设置0%、0.5%和1% 3 个梯度的赤泥施用量,利用根际袋法系统研究了赤泥对水稻（浙优12 号）根表和根际铁膜的形成及重金属（Fe、Mn、Cd）分布特征,探讨了赤泥条件下水稻根际效应对水稻Cd 吸收转运及生物量的影响.研究结果表明,赤泥显著增加了水稻的株高、根干重、秸秆干重和籽粒重;显著降低了供试水稻根部Cd 浓度、秸秆Cd 和籽粒Cd 的浓度,下降幅度分别为23.6%-40.2%,20.1%-48.8%和45.5%-103%;显著提高了水稻根表和根际铁膜中Fe、Mn 和Cd 的浓度（P 〈 0.05）,且随赤泥施用量的增加而增加.水稻根表铁膜中Fe、Mn 和Cd 浓度提高幅度分别为64.5%-107%、13.9%-43.7%和20.8%-69.9%;水稻根际铁膜中Fe、Mn 和Cd 提高幅度分别为93.8%-206%,20.1%-42.2%和17.3%-111%.与对照处理相比,添加赤泥土壤的pH 值提高程度均达到显著水平（P〈0.05）,DTPA 提取态镉含量分别降低17.9%-47.9%和26.3%-48.6%.水稻根表和根际铁膜中Cd浓度与水稻根Cd 浓度、秸秆Cd 浓度、籽粒Cd 浓度、根表和根际铁膜中的Fe 浓度和Mn 浓度呈显著正相关（P〈0.05）.结论：赤泥的添加促进了水稻的生长,且其富含铁氧化物的特性还可以促进水稻根表和根际铁膜的形成,通过铁膜中的Fe和Mn 对Cd 富集作用来减少水稻秸秆和籽粒对Cd 的吸收.因此,利用富含铁氧化物的赤泥作为钝化材料修复中低度Cd 污染稻田有望达到较好的修复和利用效果.

Recently, mild cadmium (Cd)-polluted paddy soils and ‘Cd brown rice’ seriously influence the health of Chinese people. The experimental objective is to investigate the effects of red mud on iron plaque formation on root surface and in rhizosphere and Cd uptake of rice grown in Cd-polluted soils. A pot trial with the soils with two Cd levels (2, 5 mg·kg-1) was conducted to apply red mud (RM) (0.5%, 1%) to the rice named Zheyou12 by the method of rhizosphere bag. Compared to the control (CK) without RM application, the height and biomass (root, straw and grain) were increased significantly (P < 0.05) in the RM0.5% and RM1% application under 2 and 5 mg·kg-1 Cd conditions. The soil pH was significantly (P < 0.05) increased and the DTPA-extractable Cd concentrations was remarkably decreased with the increasing RM application. The concentrations of Cd in root, straw and grain were significantly decreased with the increasing RM additions, ranging from 23.6%~40.2%, 20.1%~48.8% and 45.5%~103%. The concentrations of Fe, Mn and Cd on root surface and in the rhizosphere were significantly increased with the increasing RM application, ranging from 64.5%~107%, 13.9%~43.7% and 20.8%~69.9% on root surface, and from 93.8%~206%, 20.1%~42.2% and 17.3%~111% in the rhizosphere, respectively. Positive correlations were found between Cd concentrations on root surface and in the rhizosphere and Cd concentrations in root, straw and grain, and Fe and Mn concentrations on root surface and in the rhizosphere. Furthermore, the both Cd treatments significantly improved Fe and Mn concentrations on root surface and in the rhizosphere. Besides the specific sorption of Cd by Fe oxides in RM and the reduction of Cd availability induced by an increase in soil pH, the principal mechanism might also be due to RM-induced enhancement of the formation of iron plaque on root surface and in the rhizosphere. The concentrations of Cd, Fe and Mn in iron plaque of root surface and in the rhizosphere remarkably increased with increasing rates of RM application. The results suggest that red mud-induced enhancement of the formation of iron plaque on the root surface and in the rhizosphere of rice may be significant for the development approaches to reducing Cd accumulation in rice.