Abstract
The soil bacterial diversity is one of the most important indicators to evaluate the effect of phytoremediation. In this study, the technologies of Sequence-Related Amplified Polymorphism (SRAP) and 16S rRNA gene sequence analysis were used to evaluate the soil bacterial diversity after phytoremediation in a barren rare earth mined area. The results showed that the plant density was remarkably increased after the phytoremediation. The SRAP analysis suggested that the soil bacterial diversity declined dramatically after mining, while increased significantly in second and third year of the phytoremediation. A total of eight bacterial genera were identified by using 16S rRNA gene sequence analysis, with Arthrobacter and Bacillus as the dominant species before the mining, and Brevibacillus as the dominant species after the mining and during the first year of the phytoremediation. The Bacillus, which was a dominant type of bacteria before the mining, disappeared after mining and appeared again in the second and third years of the phytoremediation, other bacterial genera present. Principal component analysis and 16S rRNA gene analysis revealed a new bacterial type after phytoremediation that was not existed in the original mined area. The results of the present study indicated that the soil bacterial richness and genetic diversity significantly increased after the phytoremediation in the mined site.
Highlights
China is the major rare-earth resource country, where the rare-earth reserves, production, and sales were highest in the world (Wu et al 2010; Gao and Zhou 2011)
Genetic diversity analysis of soil bacteria by Sequence-Related Amplified Polymorphism (SRAP) A total of 120 single colonies from five soil sample were used to bacteria genetic diversity analysis
The percentage of polymorphism bands (PPB) and the polymorphism information content (PIC) values were increased year by year. These results indicated that the soil bacterial community in the rare-earth mined area decreased significantly after mining, and increased remarkably after the phytoremediation, even exceeded that before the ore processing (Fig. 2)
Summary
China is the major rare-earth resource country, where the rare-earth reserves, production, and sales were highest in the world (Wu et al 2010; Gao and Zhou 2011). The phytoremediation studies were conducted on the barren area of the rare earth mined sites in Heping County of Guangdong Province (Liu et al 2013), Changting County of Fujian Province (Jian 2012), Xinfeng County of Jiangxi Province (Li 2014), and Mianning County of Sichuan Province These studies have screened different plants species suitable for the mine tailings sites, and developed some remediation schemes. Some of the studies investigated the effects of various soil stress factors on the growth of Paspalum conjugatum (Yang et al 2014), the tolerance of Sorghum bicolor to rare-earth elements (Guo et al 2013), as well as the effects of Arbuscular mycorrhizae on reducing the toxicity of rare-earth elements and heavy metals and to facilitate plant growth (Chen and Zhao 2007) In these studies, phytoremediation strategies were established through field experiments or simulation experiments, and the soil structure and physiochemical properties were analyzed. The change of soil bacterial community was rarely studied in the barren area of the mined sites, which greatly limited the use of phytoremediation technologies for the improvement of rare-earth mined areas
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