<i>Cinnamomum Camphora</i> and Ground Cover Planting to Promote its Growth and Enrichment of Cd

Li-han FENG; Xiao-xiao LI; Ling LI

doi:10.13718/j.cnki.xsxb.2020.03.015

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The seedlings of ground cover plants Nephrolepis auriculata, Ophiopogon japonicus and Polygonum capitatum were used as materials, and were planted with Cinnamomum camphora seedlings respectively in solution Cd stress (0.1, 0.3, 1, 5 mg/L) (CK: Cinnamomum camphora monoculture) for 4 weeks. The biomass and the Cd content of Cinnamomum camphora seedlings and Cd content of solution were determined, and the effects on growth and Cd enrichment of Cinnamomum camphora with three ground cover plants were studied. The results show that the combination of Cinnamomum camphora-Nephrolepis auriculata and Cinnamomum camphora-Ophiopogon japonicus significantly increased the biomass of Cinnamomum camphora. When Cd was 5 mg/L, the total biomass of Cinnamomum camphora increased by 46.77% and 42.47% compared with CK, respectively. The combination of Cinnamomum camphora-Nephrolepis auriculata could significantly increase the Cd enrichment of Cinnamomum camphora. When Cd was 0.1 mg/L, the aboveground and whole plant enrichment of Cinnamomum camphora were 1.639 μg/plant and 7.351 μg/plant, which was increased by 137.88% and 77.86% compared with CK, respectively. The combination of Cinnamomum camphora-Nephrolepis auriculata and Cinnamomum camphora-P. capitatum significantly increased the transport capacity of Cinnamomum camphora to Cd. When Cd was 5 mg/L, the transfer coefficients were 0.161 and 0.138, respectively, which were 76.92% and 106.41% higher than CK. The Cinnamomum camphora-Ophiopogon japonicus combination could significantly increase the Cd removal rate of the culture solution. When Cd was 0.1 mg/L, the removal rate of Cd of Cinnamomum camphora was 68.67%, which was 50.01% higher than that of CK. It was proved that the combination of Cinnamomum camphora and three ground cover plants played a positive role in Cinnamomum camphora's growth and absorption and transport of Cd, among them, the combination of Nephrolepis auriculata and Cinnamomum camphora had the most comprehensive positive effects on Cinnamomum camphora, the combination of Ophiopogon japonicus and Cinnamomum camphora had the highest removal rate of Cd.

Corresponding author: Ling LI

Received Date: 04/11/2018

Available Online: 20/03/2020

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Abstract: The seedlings of ground cover plants Nephrolepis auriculata, Ophiopogon japonicus and Polygonum capitatum were used as materials, and were planted with Cinnamomum camphora seedlings respectively in solution Cd stress (0.1, 0.3, 1, 5 mg/L) (CK: Cinnamomum camphora monoculture) for 4 weeks. The biomass and the Cd content of Cinnamomum camphora seedlings and Cd content of solution were determined, and the effects on growth and Cd enrichment of Cinnamomum camphora with three ground cover plants were studied. The results show that the combination of Cinnamomum camphora-Nephrolepis auriculata and Cinnamomum camphora-Ophiopogon japonicus significantly increased the biomass of Cinnamomum camphora. When Cd was 5 mg/L, the total biomass of Cinnamomum camphora increased by 46.77% and 42.47% compared with CK, respectively. The combination of Cinnamomum camphora-Nephrolepis auriculata could significantly increase the Cd enrichment of Cinnamomum camphora. When Cd was 0.1 mg/L, the aboveground and whole plant enrichment of Cinnamomum camphora were 1.639 μg/plant and 7.351 μg/plant, which was increased by 137.88% and 77.86% compared with CK, respectively. The combination of Cinnamomum camphora-Nephrolepis auriculata and Cinnamomum camphora-P. capitatum significantly increased the transport capacity of Cinnamomum camphora to Cd. When Cd was 5 mg/L, the transfer coefficients were 0.161 and 0.138, respectively, which were 76.92% and 106.41% higher than CK. The Cinnamomum camphora-Ophiopogon japonicus combination could significantly increase the Cd removal rate of the culture solution. When Cd was 0.1 mg/L, the removal rate of Cd of Cinnamomum camphora was 68.67%, which was 50.01% higher than that of CK. It was proved that the combination of Cinnamomum camphora and three ground cover plants played a positive role in Cinnamomum camphora's growth and absorption and transport of Cd, among them, the combination of Nephrolepis auriculata and Cinnamomum camphora had the most comprehensive positive effects on Cinnamomum camphora, the combination of Ophiopogon japonicus and Cinnamomum camphora had the highest removal rate of Cd.

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随着我国城市化和工业化进程的加剧，土壤重金属污染日益严重^[1].镉污染在无机污染物中超标率最高^[2]，易被作物吸收并通过食物链在人体内富集，对人体健康产生极大威胁^[3].目前，土壤镉的植物修复研究广受重视，但研究对象多为种类少、生长期短的超富集植物^[4]，推广应用受到限制.木本园林植物生物量大、寿命长，对重金属表现出提取量大、固定时间长、固定效果稳定等特点^[5-6]，因而在土壤镉修复中极具应用价值.

香樟(Cinnamomum camphora)、肾蕨(Nephrolepis auriculata)和麦冬(Ophiopogon japonicus)均为西南地区常见的园林绿化植物，头花蓼(Polygonum capitatum)是西南地区常见的乡土植物.鲁艳等^[7-10]发现木本植物香樟以及地被植物肾蕨、麦冬和头花蓼等均具有一定的镉(Cd)耐受、富集和转运能力.草本地被着生地表，根系分布于土壤浅层，与根系分布较深的木本植物配植，有可能促进木本植物生长和整体增强对土壤重金属的富集作用，而这方面的研究目前还鲜有报道.本试验将香樟与肾蕨等3种草本植物组合，采用溶液培养法研究不同组合对香樟生长和富集Cd的影响.

1. 材料与方法

1.1. 试验材料

香樟、肾蕨、麦冬和头花蓼采集自西南大学校内，用半量的改良Hoagland营养液培养.

1.2. 试验方法

1.2.1. 试验材料

香樟种子于2017年12月采集，催芽；2018年3月初播种；5月初挖取高10 cm左右的幼苗进行试验.肾蕨、麦冬和头花蓼原株采于2018年3月初和4月，均在温室内分株、扦插繁育.

1.2.2. Cd胁迫水平

在营养液中添加CdCl₂·2.5H₂O(分析纯)对幼苗进行Cd胁迫处理，设4个质量浓度梯度：0.1 mg/L(0.1 Cd)，0.3 mg/L(0.3 Cd)，1.0 mg/L(1.0 Cd)和5.0 mg/L(5.0 Cd).

1.2.3. 木—草组合及试验处理

设3种木—草植物组合：香樟—肾蕨(CN)、香樟—麦冬(CO)、香樟—头花蓼(CP)，对照(CK)为香樟.每组合处理4株(木、草各2株，对照木共4株)，重复5次.

水培容器为方口塑料瓶，长9 cm、宽7.5 cm、高10 cm，容量为600 mL，用报纸和黑色不透光地膜包装瓶身，保障水培容器瓶身不透光.胁迫处理前幼苗先在去离子水中培养3 d，然后在营养液中预培养3周，待长出白色新根后开始进行Cd胁迫处理.胁迫期间，不换培养液，每天2次人工翻根换气40 min，每天用去离子水补充液面，保持液面高度5.8 cm，体积350 mL，并对幼苗同时进行光照培养.光源为红蓝光LED灯，光照强度为5000 lx(12 h/d)，昼夜温度为25/18℃，胁迫处理4周后进行生物量和Cd质量浓度测定.

1.3. 测定指标及方法

1.3.1. 香樟生物量(干质量)

将香樟幼苗地上部分与根部分离，根部在20 mmol/L EDTA-Na₂中螯合20 min，去除表面Cd²⁺，用去离子水冲洗3遍.将各部分于烘箱105 ℃杀青30 min，然后80 ℃烘至恒质量，用万分之一电子天平测质量.

1.3.2. 香樟Cd质量比的测定

将干燥香樟幼苗用植物微样粉碎机粉碎，过1 mm尼龙筛，经HNO₃-HClO₄混合消化后定容^[11]，用日立Z-5000原子吸收分光光度计测地上部和根的Cd质量比.

1.3.3. 水溶液Cd质量浓度的测定

用日立Z-5000原子吸收分光光度计测定试验起始和结束时水溶液的Cd质量浓度.

1.4. 数据处理与分析

试验数据利用Microsoft Excel 2016统计平均数，用SPSS 25.0软件对不同处理间的差异进行Duncan's多重比较，用Origin 2018作图.

转移系数(translocation factor，TF)的计算公式为^[12]：

Cd富集量(M，μg/株)的计算式为：

式中：C为香樟对应部位的Cd质量比(μg/g)；m为香樟对应部位的生物量(g).

重金属Cd去除率(修复率)的计算公式为：

3. 结果与讨论

试验结果表明，香樟与肾蕨、麦冬和头花蓼配植对其生长和富集Cd有促进作用.其中，香樟与肾蕨配植积极影响最全面，与麦冬配植Cd去除率最高.

3种草本地被植物对香樟生物量有不同程度的影响，麦冬和肾蕨促进生长的作用较明显，可能是根系分泌物对香樟的生长产生了积极影响；也可能是麦冬和肾蕨也同样大量吸收了环境中的Cd，缓解了Cd对香樟的抑制和毒害，有利于香樟的生长.

研究结果表明，草本植物(肾蕨)与香樟配植促进了香樟对Cd的吸收和转运，此类现象在其他作物中也曾被发现.蒋成爱等^[13]研究发现，东南景天与玉米和大豆的混作显著提高了其地上部分对Zn的吸收，显著降低了玉米和黑麦草对Cd和Zn的吸收；赵颖等^[14]指出，不同间作作物对玉米吸收重金属的效果不同.原因可能是因为植物根系的分泌物能影响重金属的活性或存在状态，从而影响植物对重金属的吸收^[15].由于植物种类不同，根系分泌物的种类和含量存在差异^[16]，所以不同植物组合栽培时，根系环境会随之改变^[17]，可能进而改变了香樟对重金属的吸收和转运.有研究认为，Cd在液泡中的区室化是阻止Cd长距离运输的有效途径^[18]，有可能肾蕨和头花蓼减弱了香樟根部对Cd的区室化作用，促进Cd向地上部运输.本试验表明，肾蕨和头花蓼能显著促进Cd向香樟地上部的转运，可以有效提高香樟对Cd的提取效率，此研究结果具有很大的应用价值.

本试验结果还表明，麦冬与香樟配植提高了水溶液Cd的去除率，且此组合Cd去除率均高于其余组合.麦冬对香樟吸收Cd的促进作用不明显，可能是麦冬本身的Cd吸收富集能力很强，吸收了水溶液中大量的Cd，使得CO组合的Cd去除率最高.实际应用中可利用麦冬Cd吸收量大的优势，采用定期收获再播种的方式，加快修复进程.

Figure (3) Table (2) Reference (18)

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Cinnamomum Camphora and Ground Cover Planting to Promote its Growth and Enrichment of Cd

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Cinnamomum Camphora and Ground Cover Planting to Promote its Growth and Enrichment of Cd

Corresponding author: Ling LI