镉在北京褐潮土中对玉米幼苗及其根际微生物的毒性效应

通过温室盆栽实验,研究了镉在北京褐潮土中对玉米(品种郑单958)幼苗的毒性效应及其生物富集特性,并通过聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)技术,探讨了镉对玉米根际微生物群落结构的影响。结果表明,高浓度(>100mg·kg-1)镉对玉米幼苗的生长发育有明显的抑制作用,北京褐潮土中镉引起玉米幼苗株高下降1/2的效应浓度(EC50)为654.6mg·kg-1,引起玉米根部和地上部干质量下降1/2的EC50分别为323.6和110.2mg·kg-1,玉米幼苗地上部生物量(干质量)可作为评价重金属生态毒性的适宜终点。玉米幼苗对镉有一定的吸收累积效应,镉在玉米幼苗各组织中的浓度分布为根>茎>叶,其中根部对镉有一定的富集作用(生物富集系数BAF>1)。镉污染可引起玉米根际微生物群落结构发生改变,高浓度(1000mg·kg-1)镉可导致部分微生物种群数量减少甚至完全消失,表明镉污染可对植物幼苗、植物根际微生物以及植物-微生物之间的相互作用造成重要的干扰和威胁。

Toxic Effects of Cadmium on Maize Seedlings and Rhizosphere Microbes in Fluvo-Aquic Soils of Beijing

A pot trial was carried out in green house to investigate the uptake and toxicity of cadmium (Cd) to seedlings of maize (Zea mays L.) cultivar Zhengdan 958 in fluvo-aquic soils of Beijing. PCR-DGGE analysis was performed to determine the effects of Cd on composition of rhizosphere microbe community. The results showed that Cd could stunt growth and development of maize seedlings at concentrations higher than 100 mg·kg^-1. The effective concentration (EC₅₀) causing 50% reduction of plant height was 654.6 mg·kg^-1, and the EC₅₀ for root and shoot biomass (dry weight) were 323.6 and 110.2 mg·kg^-1, respectively. The shoot biomass could serve as a suitable endpoint for assessing metal ecotoxicity to plant seedlings. Cadmium could be taken up and accumulated in both root and above-ground tissues of maize seedlings. Generally, the concentration of Cd decreased in the order: root > stem > leaves, and particularly a bioaccumulation of Cd was observed in maize root with bioaccumulation factor (BAF) larger than 1. Cadmium could exert great impacts on the composition of maize rhizosphere microbe community. The population of certain rhizosphere microbes declined under the stress of Cd, and some species might be subject to extinction at concentration of 1 000 mg·kg^-1, indicating a sever interference and threat of high-level Cd contamination to plant seedling, rhizosphere microbes, and the interaction between plant and microbes.