莴笋根际土壤中铅的有效性

采用温室栽培试验比较莴笋根际与非根际土壤pH、TOC、Pb化学形态和有效Pb含量的变化,研究根际土壤pH、TOC和Pb化学形态变化对土壤Pb有效性的影响,并为低分子有机酸作为提取剂研究土壤Pb植物有效性进行尝试.研究表明,与非根际土壤相比,莴笋根际土壤的pH降低,TOC含量增加.随着土壤Pb处理浓度的增加,根际土壤的酸化作用增强,TOC含量进一步增加.与非根际相比,根际交换态Pb含量较高.随着Pb(NO₃)₂添加量的增加,Pb的形态发生了由残渣态向碳酸盐态和交换态的转化.在土壤风干过程中,Pb的交换态、碳酸盐态和铁锰态增加.由于受到根际酸化作用和TOC结合的影响,根际土壤有效Pb含量高于非根际,并且随着Pb处理浓度的增加,有效铅含量增加.风干土壤有效Pb含量高于新鲜湿润土壤.根际土壤交换态和碳酸盐态Pb含量的变化影响根际土壤Pb有效性.与莴笋体内Pb含量的相关分析的结果表明,用低分子有机酸提取的莴笋根际新鲜湿润土壤中的Pb可以表征土壤Pb对莴笋的有效性.

Phytoavailable Lead in Rhizosphere of Lettuce

A greenhouse experiment was performed to investigate the influence of pH TOC,and fractionation of Pb on phytoavailability of Pb in the rhizosphere of lettuce.And the Low molecular-weight organic acids(LMWOAs) were used to evaluate the phytoavailability of soil Pb to lettuce.The results show that the pH is lower in the rhizosphere compared to the bulk soil,and the rhizosphere becomes more acidic with increasing Pb(NO₃)₂ applied.In contrast,the TOC content is higher in the rhizospherer compared to the bulk soil,and more TOC accumulates in the rhizosphere with increasing Pb(NO₃)₂ applied.The concentrations of different fractions in rhizosphere soils follow the order of exchangeable>carbonate bound>Fe-Mn oxide bound>organic bound>residual,and for bulk soil the order is carbonate bound>Fe-Mn oxide bound>exchangeable>organic bound>residual.Compared with bulk soils,exchangeable Pb increases significantly in rhizosphere.With increasing Pb(NO₃)₂ applied,the transformation of residual Pb to carbonate bound and exchangeable Pb may have happened and results in the accumulation of carbonate bound and exchangeable Pb.The air-drying increases the concentration of exchangeable,carbonate bound and Fe-Mn oxide bound Pb and decreases organic bound and residual Pb.Rhizosphere and bulk soils were extracted by low molecular-weight organic acids(LMWOAs) to fractionate Pb fraction of soil pools,which is considered as the phytoavailable Pb.The results show that phytoavailable Pb in rhizosphere is much higher compared to bulk soil,and phytoavailable Pb increases with increasing Pb(NO₃)₂ applied due to acidification processes and accumulated TOC in the rhizosphere.Air-drying process also increases the phytoavailable Pb.The root-induced changes of Pb availability in the rhizosphere might also be related to the Pb species,especially carbonate bound and exchangeable Pb.Correlation analysis indicates that application of wet fresh rhizosphere soils and LMWOAs should be recommended in the future study on the phytoavailability of soil Pb to lettuce.