Abstract:

The widespread issue of soil co-contamination with heavy metals and organic compounds presents a significant challenge to environmental remediation. Metal-hyperaccumulating plants can remove heavy metals from soil by absorbing and accumulating them in their tissues. However, their effects on the removal of organic pollutants in co-polluted soils, particularly the role of rhizosphere microorganisms in this process, remain unclear This study investigated the influence and mechanism of Sedum plumbizincicola on the bioremediation of phenanthrene (PHE) in cadmium (Cd)-PHE co-contaminated soils under different Cd concentrations. Analysis of the PHE degradation rates, microbial community, and abundance of PHE-degrading bacteria at different Cd levels in the soil revealed that Cd inhibited PHE degradation. The PHE degradation rates in treatments with and without S. plumbizincicola were reduced by 25.6% and 13.3%, respectively, when a Cd concentration of 10 mg∙kg⁻¹ was added. However, S. plumbizincicola significantly promoted PHE degradation in Cd-PHE co-contaminated soil at lower Cd concentrations, and increased the abundance of potential PHE-degrading bacteria in the rhizosphere soil. The average degradation rate and abundance of potential degraders were 6.77% and 0.538%, respectively, which were higher than those in the unplanted treatment. Further analysis coupled with the potential functional microbes identified by stable isotope probing (SIP) indicated that Cd inhibited the activity of certain microorganisms, such as those represented by Micrococcaceae, which are intolerant or have low Cd tolerance, thereby hindering PHE degradation in the soil. Conversely, S. plumbizincicola alleviated the toxicity of Cd to potential PHE-degrading bacteria and enriched specific PHE-degrading bacteria, such as Micrococcaceae and Ellin6067, which are plant growth-promoting bacteria in the rhizosphere. This enrichment enhanced the total abundance of potential PHE-degrading bacteria and facilitated PHE degradation in soil. Additionally, Ellin6067, KD3-93, Flavisolibacter, and Adhaeribacter have been identified as potential PHE degraders using DNA-SIP. This study provides theoretical guidance for the application of metal-tolerant or- hyperaccumulating plants in the remediation of soils co-contaminated with heavy metals and polycyclic aromatic hydrocarbons.

Key words: cadmium, phenanthrene, co-contamination, Sedum plumbizincicola, microbial community, stable isotope probing

摘要：

土壤重金属-有机物复合污染问题较为普遍，重金属超积累植物可通过吸收积累重金属至植株内，从而去除土壤中的重金属，但这类植物对复合污染土壤中有机污染物去除的影响尚不清楚，尤其是根际微生物在此过程中的作用机理仍然未知。基于此，探讨了镉-菲（Cadmium-Phenanthrene，Cd-PHE）复合污染土壤中，不同质量分数Cd处理下伴矿景天（Sedum plumbizincicola）对土壤中PHE生物消减的影响及其作用机理。对不同质量分数的土壤Cd影响下PHE的降解率、微生物群落组成、PHE潜在降解菌组成以及丰度进行分析，发现Cd会抑制PHE的降解，Cd添加量为10 mg∙kg⁻¹时种植伴矿景天与不种植处理PHE的降解率分别降低了25.6%和13.3%。而伴矿景天在土壤Cd质量分数较低时则能显著促进Cd-PHE复合污染土壤中PHE的降解，其平均降解率较未种植物处理高出6.77%。同时提高了根际土壤中PHE潜在降解菌的丰度，其平均丰度较未种植处理高出0.538%。进一步结合SIP识别到的功能微生物分析发现，Cd的存在可通过降低以Micrococcaceae为代表的不耐受或具有低Cd耐受性的功能微生物的丰度，影响这类微生物对PHE的降解过程，从而不利于土壤中PHE的降解。而伴矿景天则能缓解Cd对PHE潜在降解菌的毒害，并通过在根际显著富集Micrococcaceae和Ellin6067等植物促生菌，提高这类特定PHE潜在降解菌的丰度，进而提高根际土壤中PHE降解菌的总丰度，促进土壤中PHE的降解。此外，通过DNA-SIP技术，还探查到Ellin6067、KD3-93、Flavisolibacter和Adhaeribacter为具有PHE潜在降解功能的微生物。该研究有望为耐重金属植物或重金属超积累植物在重金属-多环芳烃复合污染土壤修复领域的应用提供理论指导。

关键词: 镉, 菲, 复合污染, 伴矿景天, 微生物群落, 稳定同位素探针