模拟干湿交替环境作用下狗牙根根系分泌物对消落带Pb的影响

Effects of Root Exudates of Bermuda Grass on Pb in the Fluctuating Zone Under Simulated Drying and Wetting Alternation Environment

为探究狗牙根根系分泌物对消落带Pb迁移能力和生物有效性的作用,通过模拟试验,选取三峡库区消落带优势植物狗牙根根系分泌的低分子量有机酸,研究在干湿交替环境作用下,根系分泌物对污染土壤及上覆水中Pb总量、土壤中Pb赋存形态的影响。结果表明:在干湿交替环境作用下,表层土壤中Pb含量不断减少,底层土壤中Pb含量不断增加;2次落干—淹水结束后,各处理表层土壤中Pb含量为混酸>柠檬酸≈乙酸>丙二酸>对照,底层土壤Pb含量为混酸>柠檬酸≈乙酸>丙二酸>对照。表层土壤中碳酸盐结合态、铁锰氧化态Pb是导致土壤总Pb含量减少的主要原因,最大减少幅度分别为24.89%和19.04%;但添加了低分子量有机酸的处理,表层土壤中铁锰氧化态、有机结合态Pb含量比对照高,可交换态Pb含量比对照低;且有机酸促进了底层土壤中碳酸盐结合态及铁锰氧化态Pb含量的增加。在2次淹水过程中,上覆水Pb含量均呈先增加后降低的趋势,低分子量有机酸抑制了土壤向上覆水释放Pb。总的来说,在干湿交替环境作用下,狗牙根根系分泌物降低了表层土壤中Pb环境风险。

In order to explore the effect of bermuda grass root exudates on migration and bioavailability of Pb in the fluctuation zone,low molecular weight organic acids secreted by bermuda grass roots of the dominant plants in the fluctuating zone of Three Gorges Reservoir area were selected,and the effects of root exudates on the total amount of Pb in contaminated soil and overlying water and the occurrence forms of Pb in soil were investigated in the dry and wet alternate environment through simulation tests.The results showed that in the wet and dry alternate environment,the Pb content in the topsoil decreased,the content of Pb in the bottom soil increased.After two times of wet and dry alternating,the Pb content in topsoil of the different treatments followed the order of mixed acid >citric acid≈acetic acid > malonic acid > control,the Pb content in the bottom soil was sorted as mixed acid > citric acid≈acetic acid > malonic acid > control.Carbonate-bound Pb and iron-manganese oxidized Pb in surface soil were the main reasons for the decrease of total Pb content,maximum reduction rates was 24.89% and 19.04% respectively.However,in the treatments added low molecular weight organic acids,the contents of Fe-Mn oxidized Pb and organic bound Pb in surface soil were higher than those in the control,while the exchangeable Pb content was lower than that of the control.Moreover,organic acids promoted the increase of contents of Pb in the carbonate bound state and Fe-Mn oxidation state in the bottom soil.During the two flooding process,the content of Pb in overlying water both increased first and then decreased,low molecular weight organic acids inhibited the release of Pb from soil to overlying water.In general,in the wet and dry alternate environment,the root exudates of bermuda grass reduced the environmental risk of Pb in topsoil.