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镉是剧毒重金属元素之一,易通过生物链在人体富集,最终可能会影响神经、生殖系统并导致癌症[1]。据我国前期调查,镉污染土壤点位超标率达到7.0%,污染情况不容乐观,城市土壤受到的Cd污染尤为突出[2-3]。由于应用成本低、环境友好等优点,以特定植物降低重金属污染的植物修复技术,近年来受到了广泛的关注[4-5]。尤其是在受污染的城市地区,兼具景观营造和生态修复的观赏植物正成为修复重金属污染土壤的关注热点[6]。
木芙蓉(Hibiscus mutabilis L.)是锦葵科 (Malvaceae)木槿属 (Hibiscus)落叶灌木或小乔木,花姿优美,为秋季优良的园林观赏树种,在四川等多地均有园林应用[7]。研究发现木芙蓉对重金属Pb具有较强耐性和富集能力,可作为修复轻度、中度Pb污染土壤的树种之一[8],但目前对于木芙蓉的Cd胁迫响应机制还鲜见文献报道。有研究表明木槿属植物木槿(Hibiscus syriacus L.)[9]、海滨木槿(Hibiscus hamabo Sieb. & Zucc.)[10]、红麻(Hibiscus cannabinus L.)[11]具有较强的Cd耐性和富集能力,推测木芙蓉可能也具有相似的能力。目前的研究更注重高浓度Cd对植物的毒害作用,对低浓度Cd下的植物响应较少关注,这与城市土壤低浓度Cd污染分布更广不符[3]。因此,以4个木芙蓉品种(‘百日华彩’、‘彩霞’、‘醉红’、‘单瓣红’)为对象,探讨不同低浓度Cd处理下(0,2.5,5,10 mg·L-1)木芙蓉的耐性和积累特性,以期为将木芙蓉作为兼具景观营造和生态修复的观赏植物应用于Cd污染的城市土壤中提供理论依据。
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如表1所示,不同浓度Cd处理下,4个品种木芙蓉生长差异明显,随着Cd浓度增加表现为低浓度(Cd2.5)促进生长,高浓度(Cd10)抑制生长。其中,在Cd2.5处理时,‘百日华彩’的生物量相对CK增加最多,根部和地上部生物量分别增加了25.00%和16.64%,根长、新枝长也较其余品种增加最多;在Cd10处理下,‘单瓣红’的生物量下降幅度最大,根部和地上部生物量分别降低21.43%和24.44%,而‘百日华彩’的生长受抑制程度最小,根部生物量降低19.44%,地上部生物量增加了1.31%,说明Cd处理下‘百日华彩’的生长相对其他品种更好。Cd处理下,木芙蓉TI值为0.76~1.17;随着Cd浓度增加,TI值降低;不同品种的TI值大小为‘百日华彩’>‘彩霞’>‘醉红’>‘单瓣红’,其中,‘百日华彩’在所有Cd浓度处理下的TI值均大于1,表明其对Cd的耐性最强,而‘单瓣红’在Cd5时TI值已小于1,在Cd10时仅为0.76,表明其对Cd相对敏感。
品种 处理 根长/cm 新枝长/cm 根部生物量/g 地上部生物量/g 总生物量/g 耐性指数TI 百日华彩 CK 13.90±0.82Bb 7.07±0.12Ca 0.36±0.04Ba 6.13±0.03Ba 6.49±0.01Ba − Cd2.5 16.40±1.82Ab 11.53±1.11Aa 0.45±0.02Ba 7.15±0.19Aa 7.6±0.2Aa 1.17±0.03Aa Cd5 17.43±1.50Ab 8.43±0.21Ba 0.53±0.06Aa 6.45±0.3Ba 6.98±0.26ABa 1.08±0.04Aa Cd10 13.27±0.12Bb 7.13±0.12Ca 0.29±0.03Ca 6.21±0.24Ba 6.5±0.27Ba 1.00±0.04Aa 彩霞 CK 16.4±1.22Ca 5.10±0.44Bb 0.34±0.05BCa 5.38±0.58ABb 5.72±0.58Bb − Cd2.5 18.37±0.59ABa 7.37±0.61Ac 0.38±0.04Ba 6.03±0.63Ab 6.41±0.63Ab 1.12±0.05Aa Cd5 19.43±0.95Aa 7.40±0.53Ab 0.46±0.01Ab 5.66±0.44ABb 6.12±0.44ABb 1.08±0.14Aa Cd10 16.93±0.61BCa 6.60±0.20Aa 0.29±0.02Ca 5.33±0.33Bb 5.62±0.35Bb 0.99±0.15Aa 醉红 CK 13.8±0.95Bb 7.37±0.67Ca 0.28±0.02Ab 5.93±0.28ABab 6.21±0.26ABab − Cd2.5 18.47±0.23Aa 9.60±0.35Ab 0.24±0.01Ab 6.32±0.53Ab 6.56±0.52Ab 1.06±0.09Aa Cd5 18.00±1.64Aab 8.23±0.06Ba 0.26±0.03Ac 6.02±0.46ABab 6.29±0.46ABb 1.02±0.12Aa Cd10 12.27±1.6Bb 5.33±0.45Db 0.24±0.03Ab 5.66±0.04Bab 5.9±0.01Bab 0.95±0.04Aa 单瓣红 CK 8.57±0.35Bc 4.87±0.21BCb 0.14±0.01Ac 5.85±0.55ABab 5.99±0.55ABab − Cd2.5 10.63±0.32Ac 6.37±0.15Ad 0.17±0.01Ac 6.2±0.28Ab 6.37±0.27Ab 1.07±0.14Aa Cd5 7.40±0.10BCc 5.50±0.70Bc 0.14±0.02Ad 5.54±0.41Bb 5.68±0.39Bb 0.96±0.14Aa Cd10 6.47±0.06Cc 4.43±0.50Cc 0.11±0.01Ac 4.42±0.37Cc 4.53±0.36Cc 0.76±0.11Bb 注:表中不同大写字母表示同一品种不同处理间差异显著(P < 0.05),不同小写字母表示同一处理条件下不同品种之间差异显著(P < 0.05),短横线(−)表示无值。
Note: In the table, different capital letters indicate significant difference among the four treatments (CK, Cd2.5, Cd5 and Cd10) for the same variety (P < 0.05). Different lowercase letters indicate significant difference between different varieties under the same treatment (P < 0.05). The short line (−) indicate no values.Table 1. Growth traits and relative tolerance index of different Hibiscus mutabilis varieties under Cd treatment
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Cd处理下,四个品种木芙蓉的叶绿素a、叶绿素b、总叶绿素和类胡萝卜素相对CK均显著降低(见图1),但不同品种降低程度不同,Cd处理下叶片色素相对CK下降幅度表现为:‘百日华彩’<‘彩霞’<‘醉红’<‘单瓣红’。植物叶片色素的高低能间接反映植物对Cd的耐受性,在Cd10处理时,‘百日华彩’的总叶绿素和类胡萝卜素分别是其余品种的1.12~2.52倍和1.16~2.17倍,说明‘百日华彩’对Cd的耐性最强。
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由图2可知,4个木芙蓉品种根部和地上部Cd含量随着Cd浓度的增加而增加,且根部Cd含量远高于地上部,分别为205.01~1089.35 mg·kg−1和27.70~188.92 mg·kg−1,根部Cd含量是地上部的2.60~13.32倍。在各Cd浓度条件下,‘百日华彩’根Cd含量最高,是其余品种的1.08~1.92倍,Cd10时‘百日华彩’根Cd含量最高,达1089.35mg·kg−1;‘彩霞’地上部Cd含量显著高于其余三个品种,是其余品种的1.21~4.16倍,Cd10时达188.92mg·kg−1。
Figure 2. Cd content in the roots (A) and shoots (B) of different Hibiscus mutabilis varieties under cadmium treatment
从图3可以看出,随着Cd处理浓度增加,木芙蓉根部和地上部Cd积累量显著增加,地上部Cd积累量显著高于根部,分别为0.17~1.01 mg·plant−1和0.04~0.32 mg·plant−1,地上部Cd积累量是根部的2.04~6.10倍,这主要是由于木芙蓉地上部的生物量远大于根部; ‘百日华彩’的根部Cd积累量显著高于其他三个品种,而‘彩霞’的地上部Cd积累量最高;不同品种木芙蓉整株Cd积累量差异显著,为0.21~1.30 mg·plant−1,品种间大小为:‘彩霞’>‘百日华彩’>‘醉红’>‘单瓣红’,‘彩霞’的整株Cd积累量分别为其余三个品种的1.00~4.49倍,Cd10时,‘彩霞’的整株Cd积累量最高,为1.30 mg·plant−1。
Figure 3. Cd accumulation in the roots (A) 、shoots (B) and whole plant (C) of
different Hibiscus mutabilis varieties under cadmium treatment 由图4所示,Cd处理下4个木芙蓉品种根部对Cd的富集系数(BCF)为56.83~115.59,其中,‘百日华彩’的富集能力最强,在各Cd浓度下均高于100,为其余三个品种的1.07~1.92倍,在Cd5浓度处理时‘百日华彩’根的富集系数最高,达115.59;Cd处理下木芙蓉的转运系数(TF)为0.08~0.38,随着Cd处理浓度的增加4个木芙蓉品种根部向地上部的转运系数逐渐下降;不同品种的转运系数在各Cd处理浓度下差异显著,大小表现为:‘彩霞’>‘百日华彩’>‘醉红’>‘单瓣红’,‘彩霞’的Cd转运系数最大,是其余品种的1.46~4.12倍。
Response of different Hibiscus mutabilis L. varieties to cadmium stress
doi: 10.12172/202303300001
- Received Date: 2023-03-30
- Available Online: 2023-10-24
- Publish Date: 2024-02-25
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Key words:
- cadmium /
- Hibiscus mutabilis L. /
- varieties /
- tolerance /
- accumulation
Abstract: In order to understand the response of different Hibiscus mutabilis L. varieties to cadmium (Cd) stress, the hydroponic experiments were conducted to investigate the growth, tolerance, leaf pigment, Cadmium (Cd) concentration, Cd accumulation, bioconcentration factor and transfer factor of four different Hibiscus mutabilis L. varieties under different Cd concentrations (0, 2.5, 5, 10 mg·L−1). The results showed that with the increase of Cd concentration, the growth of Hibiscus mutabilis L. showed a toxic hormetic effects. Basically, compared with CK (0 mg·L−1), adding Cd (treatments) increased biomass, root length and new branch length for all Hibiscus mutabilis L. varieties under low Cd concentration, but had opposite effects under high Cd concentration. Under Cd treatment, the leaf pigment concentration of all varieties were significantly lower compared with CK, and the leaf pigment concentration of ‘Bairihuacai’ species was the highest. The Cd tolerance index of Hibiscus mutabilis L. was 0.76-1.17, and ‘Bairihuacai’ species had the highest Cd tolerance index (1.00~1.17). The Cd concentration in the root of Hibiscus mutabilis L. (205.01~1089.35 mg·kg−1) was significantly higher than that in shoot (27.70~188.92 mg·kg−1). The Cd concentration in the root of ‘Bairihuacai’ species was the highest than others, and ‘Caixia’ species had the highest Cd concentration in the aboveground part. Cd accumulation in the aboveground part of Hibiscus mutabilis L. was significantly higher than that in the root, which was 0.17~1.01 mg·plant−1 and 0.04~0.32 mg·plant−1 respectively. The enrichment coefficient of Cd in Hibiscus mutabilis L. was 56.83-115.59, and the transport coefficient was from 0.08 to 0.38. Among which ‘Bairihuacai’ species had the highest Cd enrichment ability, and ‘Caixia’ species had the highest Cd transport coefficient. In conclusion, Hibiscus mutabilis L. has strong tolerance and accumulation ability under Cd pollution condition, among which 'Bairihuacai' species had the best tolerance and the strongest Cd accumulation ability among the four species, and had the greatest potential as an ornamental emediation plants for Cd restoration.