Abstract:

The mining and smelting of mineral resources can cause environment issues not only contaminating mining areas but also surrounding farmland with heavy metals through surface runoff and underground infiltration. In the mining areas, soil microorganisms have developed resistance mechanisms to heavy metals, so it is important to investigate the role of these microbes in changing the microecological environment of the plant's rhizosphere. In this study, we isolated lead (Pb)-tolerant phosphate solubilizing bacteria (PSB) from the soil in a mining area. Clear supernatants, bacteria solution, and fermentation liquid (supernatant+bacteria) were applied in rhizosphere soil of maize (Zea mays L.) to compare their effects on promoting maize growth and changes of soil Pb speciation. The screened bacteria strain is Klebsiella pasteurii, which can dissolve Ca₃(PO₄)₂ with the solubilization capacity of 26.5% by secreting acetic acid, lactic acid, tartaric acid, and oxalic acid and secrete indole-3-acetic acid (IAA). After application of the clear supernatants, bacteria solution, and fermentation liquid of K. pasteurii to the rhizosphere soil of maize, the maize's height, stem thickness, and biomass, both aboveground and belowground, were significantly improved when compared to the control group. Especially in the fermentation liquid group, maize's height, stem thickness, and biomass, both aboveground and belowground, were significantly increased by 128%, 216%, 266%, and 147%, respectively, compared to the control group. Meanwhile, the Pb accumulation in aboveground biomass of three treatment groups decreased by 68.6%, 58.1%, and 70.1%, respectively. And the Pb accumulation in roots of maize decreased by 119%, 36.7%, and 39.5%, respectively. This study indicated that the application of clear supernatants, bacteria solution, and fermentation liquid resulted in the transformation of soluble Pb into stable Pb in the rhizosphere soil. It might be because that the phosphorus released by K. pasteurii chemically reacts with soluble Pb to form stable Pb-phosphate compounds, decreasing maize absorption of Pb. We conclude that in Pb-contaminated soil, K. pasteurii can significantly promote Pb immobilization and plant's growth, and inhibit maize's absorption of Pb. Therefore, K. pasteurii plays a significant role in the remediation of Pb-contaminated soil and ensuring the food safety of crops.

Key words: Pb immobilization, Pb-contaminated mining areas, phosphate solubilizing bacteria, promoting growth, form of Pb, heavy metals, soil pollution

摘要：

矿产资源的开采、冶炼活动造成了一定的生态环境问题，土壤中可溶性重金属随着地表径流和地下渗透造成矿区和周边农田重金属污染。而矿区中土壤微生物对重金属具有一定耐性，研究微生物对植物根际微生态环境的改善作用具有重要意义。在矿区废弃地土壤中筛选耐铅（Pb）解磷菌的基础上，将含有菌株分泌物的上清液、菌液、发酵液（上清液+菌株）分别施用到玉米（Zea mays L.）根际土壤中，对比三者对玉米的促生效果及根际土壤铅的形态变化，探究解磷菌对玉米的促生机制及其对土壤铅的固化作用。所筛菌株被鉴定为巴氏克雷伯菌（Klebsiella pasteurii），其通过分泌乙酸、乳酸、酒石酸和草酸对Ca₃(PO₄)₂的溶磷率为26.5%，并能分泌生长素（IAA）。在玉米根际土壤中施用菌株的上清液、菌液和发酵液后，较对照组玉米株高、茎直径、地上与地下生物量均显著增加，其中施用发酵液组增幅最高，较对照组分别增加了128%，216%、266%、147%。同时，3个处理组中玉米地上生物量中铅含量分别降低68.6%、58.1%、70.1%，地下部铅含量分别降低119%、36.7%、39.5%。施用菌株上清液、菌液和发酵液后均使玉米根际土壤中可溶态的铅向稳定态铅转化，这可能是巴氏克雷伯菌在解离土壤磷素的过程中，其解离的磷可能与铅形成稳定态的磷铅化合物，进而降低植物对铅的吸收。由此可以得出，在铅污染土壤中巴氏克雷伯菌能够显著固化重金属铅并抑制玉米对铅的吸收，对玉米具有促生作用，因此，巴氏克雷伯菌在土壤重金属修复和保障农作物食品安全方面具有重要价值。

关键词: 铅的固化, 铅污染矿区, 解磷菌, 促生, 铅的形态, 重金属, 土壤污染