EDTA对铅锌尾矿改良土壤上玉米生长及铅锌累积特征的影响

Effects of EDTA on growth and lead-zinc accumulation in maize seedlings grown in amendment substrates containing lead-zinc tailings and soil

针对铅锌尾矿废弃地的复垦,选用玉米在5种不同尾矿砂与土壤比例的改良基质上进行盆栽试验研究。盆栽培养基质以尾矿与土壤按0∶100、25∶75、50∶50、75∶25、100∶0比例混合而成,分别标记为:TA00、TA25、TA50、TA75、TA100。研究结果表明:抑制玉米生长的主要因素是尾矿基质极端贫瘠,Pb、Zn含量过高。添加EDTA前,玉米在所有处理中都能正常生长,植株没有出现明显的毒害症状。添加EDTA后玉米生物量显著下降,并且在改良基质中尾矿所占比例越高,下降幅度越大。EDTA可以显著提高玉米对Pb、Zn的富集能力,其中对Pb的富集能力大于Zn。基质比例为50∶50时,添加EDTA后玉米对Pb、Zn的迁移量虽然比基质100∶0低,但是玉米的生物量、株高和根系各指标都比基质100∶0下降幅度小。因此,尾矿和土壤比例为50∶50的基质改良方式比较合理,可用于铅锌尾矿废弃地的复垦。

Growth of plants that absorb heavy metals is a promising approach for reclamation of contaminated soil. The aim of this study was to examine the ability of maize to absorb lead and zinc from soil, and to determine the effects of ethylenediaminetetraacetic acid （EDTA） on this process. Pot experiments were conducted in which maize seedlings were grown in amendment substrates containing Pb-Zn tailings and soil, and the effects of EDTA were determined. The ratios of Pb-Zn tailings to soil in the substrates were 0：100, 25：75, 50：50, 75：25 and 100：0, designated as TA00, TA25, TAS0, TAT5 and TA100, respectively. The main factors restricting maize growth were poor nutrition and high concentrations of Pb and Zn in the amendment substrates. Maize grew normally in test substrates without EDTA, and no apparent phytotoxicity was observed. However, biomass of maize clearly decreased with the addition of EDTA, and greater decreases in biomass were observed in maize grown in substrates containing higher proportions of Pb-Zn tailings. The decreases in average plant height with addition of EDTA were in the following order： TA100 〉 TAT5 〉 TAS0 〉TA25 〉 TA00. After addition of EDTA, the decreases were significant for the average plant height in the TA50, TA75 and TA100 substrates （P〈0.05）. The chlorophyll content-SPAD values of maize leaves decreased with increasing proportions of Pb-Zn railings in the amendment substrates. The decreases were in the following order： TA100 〉 TAT5 〉 TAS0 〉 TA25 〉 TA00. Further decreases were observed upon addition of EDTA （P 〈 0.05）. The lowest chlorophyll content-SPAD value was in the TA100 treatment, indicating that the 100% Pb-Zn tailings substrate had negative effects on photosynthetic pigments content. This was probably because the Pb-Zn tailings contained high levels of heavy metal ions, which can damage protein synthesis in k the chloroplast, leading to chloroplast decomposition. Addition of EDTA decreased the root growth, biomass, and other root indices in maize. The decreases in root length ranged from 18 to 28% , decreases in root surface area ranged from 13 to 30% , and decreases in root volume ranged from 11 to 19%. The decreases after addition of EDTA were significant for all parameters, except for root surface area in TA50 and TA75, and root volume in TA100 （P 〈 0.05 ）. The absorption of Pb and Zn by maize generally increased with greater proportions of railings in the amendment substrates. In the plants grown in TA25, TA50, TA75, and TA100, the Pb content in shoots was 4.3,6.5, 6.0 and 5.4 times that in control, respectively, and the Pb content in roots was 2.5, 3.9, 3.6 and 3.6 times that in the control, respectively, after addition of EDTA. The addition of EDTA significantly enhanced the accumulation of Pb and Zn in maize, and more Pb accumulated than Zn. Smaller amounts of Pb and Zn accumulated in maize grown in substrate containing 50% tailings and 50% soil compared with that in maize grown in substrate containing 100% railings. However, plants grown on substrate containing 50% tailings and 50% soil were healthier; that is, the values for biomass, plant height, and root indices were higher than their respective values in maize grown in substrate containing 100% tailings. Therefore, we propose that the amendment of 50% soil to tailings is reasonable for reclamation of Pb-Zn tailing waste lands.