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土壤重金属污染是指人类在生产活动中将大量重金属带入土壤,严重破坏土壤生态系统的现象[1]。土壤重金属易在食用作物中富集,通过食物链在人体蓄积,严重危害人体健康[2]。在农田土壤重金属污染中,镉 (Cd) 污染是危害最严重的一种[3]。目前,土壤Cd污染修复技术主要分为物理、化学和生物修复技术。植物修复技术成本低、生态友好、易被大众接受,但其修复周期长,修复效果受植物特性如根系分布深度等的限制而存在一定局限性[4]。电动修复因其修复周期短、去除率高、能同时去除多种污染物等优点而成为一种具较好应用前景的重金属污染土壤修复技术[5]。施加直流电场时,土壤中OH−和H+分别向阴极、阳极迁移积累,造成电极处附近极化现象[6]。而交流电场不会发生土壤pH的剧烈变化,并能改善土壤均匀性[7]。将交流电场和植物修复相结合,可以通过强化植物生长、提高植物吸收重金属能力或是提高土壤中重金属的有效性来提高修复效率[8]。
已有研究表明,施加交流电场可以促进龙葵 (Solanum nigrum L) [9]、褪色柳 (Salix discolor) [10]、东南景天 (Sedum alfredii Hance) [11]、莴苣 (Lactuca sativa) [12]等植物的生长,加强Cd在植物体内的积累。除了电场类型外,电场频率也是重要的影响参数。在较短时间内,交流电场频率由50 Hz提升到400 Hz过程中,土壤重金属的浸出质量浓度有增加的趋势[13]。预试验也显示相似结果,通过土壤培养的试验方法,设置电场频率为0~400 Hz,研究电场频率对土壤Cd活性的影响,结果显示电场频率为300 Hz时,土壤有效态Cd质量分数提高最明显,为电动修复技术的优化提供了参考。HE等[14]研究发现1 Hz脉冲电场作用可以提高玉米根系生物量。此外,低频 (60 Hz) 交流电场也能促进拟南芥地上部的增长[15]。然而较高电场频率对植物生长及土壤重金属的修复作用还有待研究。
柳树以其快速生成深根系统、高生物量、高蒸腾速率和能富集重金属等优点,在重金属污染修复实践中越来越受到重视[16]。重金属Cd超积累植物东南景天生长速率较快、富集Cd能力强,是理想的植物修复材料[17],但其为浅根系植物。植物混种系统可以丰富土壤生物群落,有利于互补作物生长和改善土壤健康[18],柳树和东南景天混种能够增加植物对地面空间的利用,从而可能促进土壤修复效率的提高。先前的研究表明,交流电场促进了柳树、东南景天对土壤Cd的吸收积累[11, 19-20]。因此,本研究通过盆栽试验的方法,探讨不同的交流电场频率 (低频50 Hz,高频300 Hz) 对竹柳3号 (Salix sp.) 和东南景天混种条件的土壤理化性质、Cd有效性、植物生长和Cd吸收积累能力的影响,为土壤重金属污染治理提供新思路。
交流电场频率对柳树-东南景天混栽修复镉污染土壤的影响
Effect of AC electric field frequency on remediation of cadmium contaminated soil by willow- Sedum alfredii Hance mixed planting
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摘要: 单一植物吸收的方法修复镉 (Cd) 污染土壤效果欠佳,交流电场联合植物可以更好地提高土壤Cd污染的治理效率。通过优化电场频率等参数可以提高土壤Cd的移动性,促进植物吸收土壤Cd。采用土壤盆栽试验的方法,研究交流电场频率 (50、300 Hz) 对竹柳3号和东南景天混种条件下土壤理化性质、Cd有效性、植物生长和Cd吸收积累能力的影响。与对照 (没有施加电场) 相比,300 Hz电场处理的土壤pH值显著降低了0.13。电场频率的提高显著提升了土壤Cd的有效性,300 Hz频率电场处理的土壤有效态Cd质量分数显著高于对照35.00%。交流电场促进了植物生长,柳树和东南景天的株高、生物量、叶片SPAD值及根系形态指标在外加50、300 Hz交流电场时均得到提高。交流电场降低了柳树各部分和东南景天地下部Cd质量分数,其中50 Hz处理柳树叶片、枝条、树干、根系和东南景天地下部Cd质量分数较对照分别降低22.16%、29.82% (P<0.05) 、1.49%、15.91% (P<0.05) 、31.81% (P<0.05) 。相反,电场频率的提高有利于东南景天地上部Cd质量分数增加,50、300 Hz处理东南景天地上部Cd质量分数较对照分别增加43.37%、55.18% (P<0.05) 。交流电场提高了植物对土壤Cd吸收积累,但不同的电场频率对植物Cd修复效率影响不同,50、300 Hz交流电场下植物地上部分总Cd积累量较对照分别显著增加24.04%、21.24%。从这2种植物上看,50 Hz交流电场更能提高柳树Cd修复效率,300 Hz交流电场更提高能东南景天Cd修复效率。本试验装置成本较低,修复效果较好,对于电场频率增强植物修复Cd效率具有很大参考价值,有较好的应用前景。Abstract: The single plant uptake method for remediation of cadmium (Cd) contaminated soil is often low efficient, while alternating current (AC) electric field combined with plants can be better for soil Cd contamination. By optimizing parameters such as electric field frequency can improve the mobility of soil Cd, promote plant uptake of soil Cd. A soil pot experiment was conducted to study the effects of (AC) electric field frequency (50 and 300 Hz) on soil physical and chemical properties, Cd availability, plant growth and Cd absorption and accumulation under the mixed planting conditions of willow (Salix sp.) and Sedum alfredii Hance. Compared to the control treatment (without application of AC electric field), the 300 Hz frequency electric field treatment significantly reduced the soil pH value by 0.13 unit. The increase of electric field frequency significantly improved the availability of Cd in soil, and the soil available Cd concentrations of 300 Hz frequency electric field treatment was significantly higher than that of the control by 35.00%. The plant height, biomass, leaf SPAD value and root morphology parameters of willow and Sedum alfredii Hance were all improved when 50 Hz or 300 Hz AC electric field was applied. The AC fields reduced Cd concentrations in all parts of willow and in the underground part of Sedum alfredii Hance. The Cd concentrations in the willow leaves, branches, trunks, roots and underground parts of Sedum alfredii Hance treated with 50 Hz decreased by 22.16%, 29.82% (P<0.05), 1.49%, 15.91% (P<0.05) and 31.81% (P<0.05), respectively, compared with the control. The Cd concentrations in the aboveground part of Sedum alfredii Hance increased by 43.37% and 55.18% (P<0.05) in the 50 Hz and 300 Hz treatments, respectively, compared with the control. The increase of electric field frequency improved plant uptake of soil Cd and the efficiency of soil Cd phytoremediation changed with the applied electric field frequency. The total Cd accumulation in the aboveground parts of plants under 50 Hz and 300 Hz AC fields increased significantly by 24.04% and 21.24%, respectively, compared to the control. In terms of the tested two plants, the 50 Hz AC field improved the Cd remediation efficiency of willow more than that of the 300 Hz, and the 300 Hz AC field improved the Cd remediation efficiency of Sedum alfredii Hance more more than that of the 50 Hz. The experimental setup had a low cost and high restoration efficiency, providing valuable reference for using electric field frequency to enhance phytoremediation efficiency for Cd, with promising application prospects.
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Key words:
- AC electric field /
- electric field frequency /
- phytoremediation /
- cadmium /
- soil
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表 1 不同处理对土壤基本理化性质和有效态Cd的影响
Table 1. Effects of different treatments on basic physical and chemical properties and available Cd of soil
处理组 pH AK/ (mg·kg−1) AN/ (mg·kg−1) AP/ (mg·kg−1) SOM/ (g·kg−1) ACd/ (mg·kg−1) CK 7.40±0.01a 48.00±3.61b 170.98±4.36a 20.80±6.41a 48.20±2.48a 0.20±0.01b 50Hz 7.40±0.03a 47.00±5.00b 167.03±4.40a 25.92±5.55a 45.31±2.31a 0.22±0.01b 300Hz 7.27±0.04b 59.00±1.00a 166.24±5.48a 17.38±1.28a 44.85±1.34a 0.27±0.03a 注:同列数据后不同小写字母代表不同处理间达到显著水平 (P<0.05) 。 表 2 不同处理对植物生物量的影响
Table 2. Effects of different treatments on plant biomass
g·株−1 处理组 柳树干重 东南景天干重 叶片 枝条 树干 根系 整株 地上部 地下部 整株 CK 2.47±0.08b 1.30±0.03b 5.10±0.04b 0.72±0.04b 9.58±0.16b 0.38±0.01b 0.06±0.01b 0.44±0.01b 50Hz 3.83±0.94a 2.04±0.38a 6.04±0.40a 0.82±0.02a 12.74±1.56a 0.41±0.01ab 0.07±0.00a 0.48±0.01a 300Hz 3.15±0.27ab 1.65±0.15ab 5.80±0.22a 0.80±0.03a 11.40±0.61ab 0.43±0.03a 0.08±0.01a 0.51±0.03a 表 3 不同处理对植物根系形态的影响
Table 3. Effects of different treatments on plant root morphology
植物类型 处理组 根系长度/cm 根系表面积/cm2 根系直径/mm 根系体积/cm3 根尖数 柳树 CK 1363.43±154.86b 453.72±69.32b 1.15±0.13a 13.06±2.74a 6193.00±1136.34b 50 Hz 1853.87±262.70a 482.89±82.76ab 1.02±0.13a 11.50±2.32a 7299.00±1151.26ab 300 Hz 1881.06±54.72a 633.98±142.02a 1.08±0.25a 14.27±6.70a 8183.67±1179.85a 东南
景天CK 291.08±37.13a 36.16±6.10a 0.39±0.03a 0.36±0.08a 3787.50±535.05a 50 Hz 307.34±57.43a 36.76±4.62a 0.39±0.06a 0.36±0.09a 3724.40±574.26a 300 Hz 295.13±28.80a 33.97±4.86a 0.38±0.06a 0.33±0.06a 4049.00±570.39a 表 4 不同处理对植物各部位Cd质量分数的影响
Table 4. Effects of different treatments on Cd concentrations in different parts of plants
mg·kg−1 处理组 柳树 东南景天 叶片 枝条 树干 根系 地上部 地下部 CK 11.95±0.81a 16.87±1.08a 5.36±1.30a 8.61±0.15a 21.93±2.40b 24.02±1.40a 50 Hz 9.30±1.29a 11.84±0.61b 5.28±0.38a 7.24±0.13b 31.44±6.43ab 16.38±1.85b 300 Hz 10.59±2.71a 13.91±1.41b 5.27±0.73a 7.01±0.32b 34.03±6.19a 21.17±1.29a 表 5 不同处理对植物Cd积累量的影响
Table 5. Effects of different treatments on Cd accumulation in plants
μg·株−1 处理组 柳树Cd积累量 东南景天Cd积累量 叶片 枝条 树干 地上部 根系 地上部 地下部 CK 29.51±2.89a 21.87±1.82a 27.28±6.44a 78.65±3.88b 6.20±0.31a 8.34±0.80b 1.36±0.08b 50 Hz 35.55±10.37a 23.96±3.28a 31.95±3.52a 91.46±16.04a 5.96±0.09a 12.79±2.26ab 1.20±0.12b 300 Hz 32.98±6.39a 22.85±2.19a 30.46±3.28a 86.29±8.28ab 5.58±0.07b 14.60±3.51a 1.70±0.09a -
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