Abstract:

Tailings are an oligotrophic environment with high concentrations of metal(loid)s, including arsenic, antimony, chromium, zinc and copper. In addition, nitrogen deficiency severely hinders the development of bioremediation strategies by plants and microorganisms. Nitrogen-fixing bacteria can provide available nitrogen to plants as well as microorganisms, which promotes tailing ecological remediation. However, the amount of isolated nitrogen-fixing bacteria from tailings is limited. Therefore, in this study, seven strains of nitrogen-fixing bacteria were isolated from the Huangjia tailings in Xupu County, Huaihua, Hunan Province, and strain PC-3 showed the highest nitrogen-fixing enzyme activity (7133.71 μmol·h^-1·mL^-1). G6, L31 and PC-3 could produce indoleacetic acid as well as siderophores and were tolerant to high concentrations of arsenic. Most strains grew well at neutral pH, while G6 and L2+2 showed the best growth trend at pH 9. The seven strains were classified as Brevundimonas (G15, G18), Xanthobacter (L31), Sphingobium (L2+2), Pseudomonas (PC-3), Mycobacterium (G6), and Rhodococcus (L45) based on their 16S rRNA sequences. Pot experiments were carried out to analyze the plant-promoting potential of isolated strains. Compared with the control group, the treatments inoculated with L2+2 and L31 significantly increased the length of plant roots and stem height, with the inoculation of the L31 strain promoting the plant root length and stem length by 130% and 93%, respectively. It also significantly increased the dry weight of plant roots and stems, with the inoculation of L2+2 promoting the plant root and stem dry weight by 260% and 188%, respectively. The treatments inoculated with G6 and L31 significantly increased the nitrogen content of the roots and stems, of which G6 had the most significant effect, which increased the nitrogen content in roots and stems of plants by 406% and 131%, respectively. Taken together, L2+2, L31 and G6 have a greater potential to promote plant growth and play an important role in obtaining nutrients and promoting ecological succession in tailings, and can be used as good candidates for biofertilizer to promote the restoration of tailings.

Key words: tailings hazard, nitrogen fixing bacteria, heavy metal pollution, plant growth promotion, ecological remediation

摘要：

尾矿是一种寡营养环境，含有大量重金属元素，然而营养元素的缺乏，尤其是氮素的缺乏严重阻碍了尾矿生物修复策略的发展。固氮菌可为植物提供可利用性氮，促进尾矿生态修复。然而，目前关于栖息在尾矿中固氮菌的分离研究较少。采用无氮培养基和稀释涂布平板分离法，从湖南怀化溆浦县黄家尾矿分离出7株具有固氮功能的菌株，结果表明，PC-3的固氮酶活性最高（7133.71 μmol·h^-1·mL^-1）。IAA、金属抗性和铁载体定性测定结果表明，G6、L31和PC-3同时具备有IAA特性、铁载体和金属抗性的能力。同时研究了菌株的最适生长pH，结果表明大部分菌株在pH偏中性下生长较好，但G6、L2+2在pH=9的条件下生长趋势最好。16S rRNA测序结果表明，上述7株菌分别为Brevundimonas（G15、G18），Xanthobacter（L31），Sphingobium（L2+2），Pseudomonas（PC-3），Mycobacterium（G6），Rhodococcus（L45）。为了进一步探究尾矿固氮菌的植物促生潜力，进行了盆栽试验。与对照组相比，接种L2+2、L31菌株显著提高了植物根长和茎长，其中L31菌株使植物根长和茎长分别增长了130%、93%；接种菌株也显著提高了植物根和茎的干质量，其中接种L2+2处理植物的根、茎的干质量分别增长了260%、188%；接种G6、L31处理植物根和茎的氮含量显著增加，效果最显著的是G6，增长量分别达到406%、131%。结果表明，L2+2、L31和G6具有较大的植物促生潜力，在获取营养物质和促进尾矿的生态演替方面发挥重要作用，可作为生物肥料的良好候选菌株，以促进尾矿生态环境的修复。

关键词: 尾矿危害, 固氮菌, 重金属污染, 植物促生, 生态修复