水淹生境下秋华柳对镉污染土壤研究修复能力

以耐水淹和耐重金属的秋华柳（Salix variegata）作为试验材料，从土壤角度出发，探究秋华柳在水淹条件下对镉污染土壤的修复能力。设置无植物和种植秋华柳两个处理组，分别对两组设置两个水分处理组：正常供水组（CK）及土壤水淹组（FL），4个镉浓度处理组：对照组（0 mg/kg）、低浓度（0.5 mg/kg）、中浓度（2 mg/kg）及高浓度（10 mg/kg）。分别于处理后的第30天和第60天对各处理组的土壤和水淹组水样进行取样。试验结果表明：（1）镉处理浓度越高，土壤中镉活性态浓度越高，生物毒性越强。（2）水淹显著降低土壤活性态Cd浓度（P < 0.05），增大土壤修复难度。（3）种植秋华柳对30d土壤Cd全量及各形态镉浓度均无显著影响（P > 0.05）；对第60天正常供水和水淹组土壤中交换态、碳酸盐结合态的镉浓度以及60d水淹组土壤Cd全量均有显著影响（P < 0.05）。（4）秋华柳种植显著降低土壤Cd迁移系数，30d正常供水组、水淹组以及60d正常供水组和水淹组平均降幅分别为2.0%、4.12%、9.71%、9.32%。处理时间过短和试验用苗生物量小可能是秋华柳对土壤全量Cd影响不大的主要原因，但秋华柳均显著降低正常供水和水淹组土壤迁移系数且二组降幅差异不大。研究表明：水淹生境下，秋华柳对Cd污染的土壤仍有较好的修复能力。

The remedial capability of Salix variegate for Cd-contaminated soil under flooding environments

The altered water regime in the Three Gorges Reservoir of the Yangtze River, China, has caused many serious environmental problems. Among them, cadmium pollution is serious, so vegetation restoration and phytoremediation of Cd-contaminated soil is fundamental in this region. The soil moisture regime of the soil is an important factor for the physical, chemical, and biological properties of soil. The bioavailability of heavy metals will be reduced under environmental flooding, making it difficult to remove the heavy metals during flooding. Research has shown that Salix variegata can tolerate both flooding and heavy metal stress. Therefore, S. variegata could be a suitable species to restore the vegetation and remedy Cd-contaminated soil in the Three Gorges Reservoir Region. To explore the phytoremediation of Cd-contaminated soil by S. variegata under flooding, factorial experimental treatments included two water regimes and four Cd concentrations. The water treatments included ambient water supply (CK) and light flooding (FL). The cadmium additions included control (0 mg/kg), low concentration (0.5 mg/kg), middle concentration (2 mg/kg), and high concentration (10 mg/kg), and each treatment involved a group of planted S. variegata shoots and a reference group without plants. Soil and water samples were collected 30 and 60 days after the start of the treatments. A sequential extraction was used in this research. The weakly bound fractions of Cd (exchangeable and carbonate-bound) were considered easy to mobilize, so they possibly presented a potential risk to the environment. The mobility factor (MF) was used to describe Cd behavior in soil. The results showed that: (1) With increasing Cd concentration in the soil, the labile fractions of Cd increased significantly, meanwhile the Cd bioavailability increased significantly, and the environmental risk could be increased significantly; (2) Water treatment significantly affected the speciation of Cd in the soil, and the MF values under the flooding treatment were much less than those under the ambient water treatment at days 30 and 60 of the experiment (P < 0.05). Furthermore, the phytoremediation of Cd-contaminated soil under environmental flooding was very different from that of the soil under ambient water supply. (3) S. variegata did not affect the total Cd concentration or Cd speciation of the soil samples taken on day 30 of the experiment, whereas it significantly reduced the total Cd concentration of the soil day 60 under the FL treatment. The exchangeable and carbonate-bound Cd concentrations of soil from both the CK and FL treatments on day 60 were also significantly affected by S. variegata. (4) The MF value of the soil samples was significantly reduced by S. variegata compared with the non-planted groups, and the average decline was 2.0%, 4.12% in treatments of PCK and PFL on day 30 of the experiment, and 9.71%, 9.32% in treatments of PCK and PFL on day 60 of the experiment, respectively. There are two primary reasons explaining why the total Cd concentration of the soil samples was not considerably affected by S. variegata shoots: (1) The duration of the incubation experiment was too short; (2) the biomass of the S. variegata shoots was relatively small. However, S. variegata significantly reduced the MF value both in the ambient water and flooding treatment, but did not differ significantly between both treatments. In conclusion, S. variegata could be a suitable species for the phytoremediation of Cd-contaminated areas under environmental flooding.