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邻苯二甲酸正二丁酯 (din-butyl phthalate,DBP) 是邻苯二甲酸酯 (phthalic acid esters,PAEs) 的一种,在我国农田土壤中被普遍检出[1-2]。土壤中的DBP能被作物吸收累积,从而对农产品安全和人体健康构成潜在威胁[3-4]。虽然目前国内外广泛开展了对污染土壤修复的研究,提出了许多较为实用的修复方法,但从目前我国实际情况来看,通过选育吸收污染物少和/或在可食部位污染物积累少的作物品种,降低污染物进入食物链的风险,仍是我国中低度污染土壤安全利用的重要途径[5-7]。
研究表明,植物根系分泌物能促进土壤颗粒或土壤-植物界面中的有机污染物的吸附/解吸行为,从而改变其被植物吸收的程度[8-11]。其主要机理是根系分泌物中的低分子有机酸 (含有1~6个碳原子和1~3个羧基的短链碳化合物 (分子量<250) ) 结合土壤阳离子,促进通过阳离子键与矿物连接的有机污染物的解吸;或/和破坏有机污染物与土壤矿物结合的桥键,增加土壤可溶性有机质,促进有机污染物的解吸[12-16]。GAO等[17-18]的研究表明,黑麦草 (Lolium multiflorum) 根系分泌物中的低分子有机酸可以促进土壤吸附态多环芳烃 (polycyclic aromatic hydrocarbons,PAHs) 转变为可提取态PAHs,从而提高对其的吸收累积。向日葵 (Helianthus annuus) 地上部邻苯二甲酸邻苯二甲酸二 (2-乙基己基) 酯 ( (di-(2-ethylhexyl) phthalate,DEHP) ) 的含量随土壤柠檬酸添加浓度的增加而增加[11]。XIANG等[15]基于核磁共振光谱、紫外光谱和对金属离子、铁/铝有机金属络合物和溶解有机碳的分析,证实了生菜根系分泌物中的草酸可以通过增强土壤金属离子、铁铝氧化物和有机物的溶解,形成草酸盐-金属络合物,提高土壤全氟辛烷磺酸 (perfluorooctanoic acid,PFOA) 的解吸,从而导致不同品种生菜对PFOA的吸收累积程度不同。
根系分泌物中低分子有机酸对土壤有机污染物解吸行为的促进作用不仅是有机污染土壤植物修复的理论依据[17-18],也可作为筛选有机污染物低累积作物品种的科学依据[15,19]。XIANG等[15]和DU等[19]分别对比研究了PFOA高/低吸收累积型生菜和PAEs高/低吸收累积型水稻根系分泌物中低分子有机酸组成特征及其对土壤PFOA和PAEs的解吸差异,以及这种差异与生菜和水稻中PAEs和PFOA含量的相关性,研究结果表明,根系分泌物中低分子有机酸种类和质量浓度的差异是导致不同品种生菜和水稻中PFOA和PAEs含量的重要因素。因此,本研究选取前期筛选出的DBP高/低累积型菜心品种,采用溶液培养方法,对比研究DBP污染下2种菜心根系分泌物中低分子有机酸的组成特性及其对土壤DBP解吸的影响,为DBP低累积作物品种的筛选提供科学依据。
2种菜心根系分泌物低分子有机酸组成特征及对土壤邻苯二甲酸正二丁酯解吸的影响
Characteristics of low molecular organic acid composition in the root exudates of two cultivars of Brassica parachinensis L. and their impacts on DBP desorption in soil
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摘要: 为探究邻苯二甲酸正二丁酯 (DBP) 高/低累积型菜心对DBP吸收累积差异的机理,采用溶液培养和室内批量实验方法,对比研究DBP污染下DBP高/低累积型菜心根系分泌物中低分子有机酸组成特征及其对土壤DBP解吸的影响。研究结果表明,2种菜心根系分泌物中均检测出甲酸、乙酸、草酸和苹果酸,其中草酸和苹果酸为2种菜心根系分泌物中主要的低分子有机酸,其在2种菜心根系分泌物中的质量浓度分别为1.56~9.28和1.06~15.38 mg·L−1。总体来看,特青根系分泌物中低分子有机酸的质量浓度低于油青。添加2种菜心根系分泌物土壤DBP的解吸率分别为45.8%~81.1% (油青) 和34.0%~52.5% (特青) ,显著高于添加蒸馏水处理 (17.0%) ,特青根系分泌物对土壤DBP的解吸率显著低于油青。相关性分析表明,2种菜心根系分泌物对土壤DBP的解吸程度与其草酸或苹果酸质量浓度相关性较弱 (r<0.146,P>0.05) ,这说明低分子有机酸不是2种菜心根系分泌促进土壤DBP解吸作用的主要因素。本研究结果可为DBP低累积作物品种的筛选提供参考。Abstract: To explore the mechanisms for different absorption and accumulation of the high/low DBP(din-butyl phthalate)-accumulation Brassica parachinensis L. cultivars for DBP, this study used solution culture and indoor batch experiments to compare the composition characteristics of low molecular organic acid in root exudates of high/low DBP-accumulation Brassica parachinensis L and their effects on the desorption of DBP in soil. The results showed that formic acid, acetic acid, oxalic acid, and malic acid were detected in the root exudates of two cultivars of Brassica parachinensis L., among which oxalic acid and malic acid were the main low-molecular organic acids in the root exudates of the two cultivars. The concentrations of oxalic acid and malic acid were 1.56~9.28 and 1.06~15.38 mg·L−1, respectively, in the root exudates of the two cultivars. Overall, the mass concentrations of low-molecular organic acids in the root exudates of Teqing were significantly lower than those of Youqing. The desorption percentages of DBP in soil supplemented with the root exudates of the two cultivars were 45.8%~81.1% (Youqing) and 34.0%~52.5% (Teqing), which were significantly higher than those supplemented with distilled water (17.0%). The desorption percentages of the root exudates of Teqing were significantly lower than those of Youqing. Correlation analysis showed that the effects of root exudates of the two cultivars on desorption percentages of DBP from soil were weakly correlated with the mass concentrations of oxalic acid or malic acid in the root exudates (r<0.146, P>0.05), indicating that low-molecular organic acids were not major factors in promoting DBP desorption from soil by the root exudates of the two cultivars. The research conclusions provide scientific basis for the screening of low DBP-accumulation crop species.
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表 1 不同生长期2种菜心根系分泌物的pH值
Table 1. The pH values of root exudates of two cultivars Brassica parachinensis L. at different growth stages
菜心品种 DBP质量浓度/
(mg·L−1)pH值 第12 d 第32 d 第48 d 油青 0 (对照) 5.54±0.05a 5.66±0.09a 5.99±0.01b* 20 5.67±0.10a 5.76±0.00a 6.10±0.02a 50 5.58±0.02a 5.68±0.04a 6.13±0.09a 特青 0 (对照) 5.60±0.09a 5.72±0.06a 6.09±0.04b 20 5.63±0.05a 5.74±0.04a 6.17±0.04a 50 5.74±0.11a 5.80±0.13a 6.20±0.02a 注:表中数据为平均值 (n=3)±标准误。同一品种菜心同一生长阶段数据标有相同字母者表示差异不显著 (P>0.05) 。 表 2 2种菜心根系分泌物对土壤中DBP的解吸率
Table 2. Desorption percentages of DBP in soil by the root exudates of two cultivars of Brassica parachinensis L.
添加溶液 DBP质量浓度/
(mg·kg−1)DBP解吸率/% 第12 d 第32 d 第48 d 蒸馏水 — 17.2±0.5d 17.8±1.0e 17.6±0.3d 油青根系分泌物 0 54.1±1.4b 51.0±2.3cd 45.8±2.0b 20 55.8±1.6b 60.9±1.3b 47.3±1.9ab 50 65.4±1.4a 81.1±2.5a 52.6±2.6a 特青根系分泌物 0 35.0±1.0c 45.8±2.2d 34.0±2.9c 20 35.5±1.1c 47.3±0cd 35.4±0.5c 50 37.0±1.1c 52.5±2.0c 36.0±1.5c 注:表中数据为平均值(n=3)±标准误。同一列含有相同字母者表示差异不显著 (P>0.05) 。 表 3 低分子有机酸对土壤DBP的解吸率
Table 3. Desorption rate of DBP in soil by low molecular organic acids
低分子有机酸种类 质量浓度/(mg·L−1) 解吸率/% 草酸 0 17.5±0.4e 1 26.8±1.2d 2 37.0±0.9c 5 43.8±0.8b 10 48.5±0.9a 苹果酸 0 17.5±0.4d 2 22.0±0.7c 4 25.5±0.9b 6 26.2±0.7b 8 43.8±0.6a 注:表中数据为平均值(n=3)±标准误。同一种低分子有机酸数据含有相同字母者表示差异不显著 (P>0.05) 。 -
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