镉对超积累和非超积累生态型东南景天内生细菌多样性的影响

Impacts of cadmium on the diversity of endophytic bacteria associated with hyperaccumulating and non-hyperaccumulating ecotypes of Sedum alfredii

摘要:

重金属胁迫对植物内生细菌群落结构的影响在很大程度上是未知的，目前也很少有研究超积累植物内生细菌的群落结构与多样性对根际土壤中重金属的响应。[目的] 探索在不同镉污染水平下，超积累（HE）和非超积累生态型（NHE）东南景天的根系、茎和叶片中内生细菌的群落结构与多样性的变化及其差异性，试图从植物-内生菌之间的相互关系的角度补充解释2种生态型东南景天对有效态镉忍耐和积累能力的差异。[方法] 采用Illumina新一代测序方法分析了在不同Cd²⁺浓度土壤上生长的2种生态型东南景天根、茎和叶中的内生细菌群落结构。[结果] 高浓度Cd²⁺抑制NHE东南景天的生长，内生细菌的丰富度和多样性也降低；然而，高浓度Cd²⁺促进HE东南景天的生长，茎和根系内生细菌的丰富度增加。在3种土壤上，2种生态型东南景天叶片、茎和根系内生细菌均以变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）、拟杆菌门（Bacteroidetes）和放线菌门（Actinobacteria）占优势。随着土壤中Cd²⁺浓度的增加，HE东南景天叶片中Gammaproteobacteria纲、Negativicutes纲和Clostridia纲的相对丰度显著增加，茎中Alphaproteobacteria纲的相对丰度显著增加，Clostridia纲的相对丰度显著减少；NHE东南景天叶片中Alphaproteobacteria纲、Gammaproteobacteria纲和Clostridia纲的相对丰度没有显著变化，茎中Negativicutes纲的相对丰度显著减少，根系中Betaproteobacteria纲和Clostridia纲的相对丰度显著减少，Negativicutes纲却显著增加。在高Cd²⁺污染土壤（50 mg/kg）上，HE东南景天叶片中Sphingomonas属和茎中Veillonella属的相对丰度均大于NHE，且HE东南景天根系内生细菌的第一、第二、第三优势菌Veillonella、Sphingomonas、Prevotella属细菌均没有出现在NHE东南景天根系。[结论] 土壤Cd²⁺污染水平对2种生态型东南景天叶、茎、根中的内生菌群落结构有显著影响。

Abstract:

The effects of heavy metal stress on the community structure of endophytic bacteria in plants are not well understood. To date, few studies have investigated the response of community structure and diversity of endophytic bacteria in hyperaccumulating plants to heavy metals present in soil rhizosphere. [Objective] The objectives of this study were to explore the changes and differences in community structure and diversity of endophytic bacteria in roots, stems, and leaves of hyperaccumulating (HE) and non-hyperaccumulating (NHE) ecotypes of Sedum alfredii under different levels of Cd²⁺ contamination; as well as to explain their differences in ability to tolerate and accumulate the available cadmium by the two ecotypes of Sedum alfredii, based on the mutual relationship between plant and endophyte. [Methods] The community structures of endophytic bacteria in the roots, stems, and leaves of the two ecotypes of Sedum alfredii grown on soils with different Cd²⁺ concentrations were analyzed by Illumina high-throughput sequencing technique. [Results] High concentrations of Cd²⁺ inhibited the growth of NHE Sedum alfredii and decreased the richness and diversity of endophytic bacteria, whereas it promoted the growth of HE Sedum alfredii and increased the richness of endophytic bacteria in stems and roots. Among the three tested soils, the endophytic bacteria in leaves, stems, and roots of two ecotypes of Sedum alfredii were all dominated by Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. For HE Sedum alfredii, the relative abundances of Gammaproteobacteria, Negativicutes, and Clostridia in leaves as well as Alphaproteobacteria in stems increased significantly with the soil Cd²⁺ concentration, whereas the relative abundances of Clostridia decreased significantly. For NHE Sedum alfredii, with the increase in soil Cd²⁺ concentration, the relative abundances for Alphaproteobacteria, Gammaproteobacteria, and Clostridia in leaves did not show significant change, while those for Negativicutes in stems as well as Betaproteobacteria and Clostridia in roots decreased significantly, and those for Negativicutes in roots increased significantly. In highly Cd²⁺-contaminated soils (50 mg/kg), the relative abundances of Sphingomonas in leaves and Veillonella in stems of HE Sedum alfredii were higher than those for NHE Sedum alfredii. Meanwhile, the first, second, and third predominant endophytic bacteria (i.e., Veillonella, Sphingomonas, and Prevotella) that were present in the roots of HE Sedum alfredii did not appear in roots of NHE Sedum alfredii.[Conclusion] The Cd²⁺-contamination level in soils had significant impacts on the community structure of endophytic bacteria in leaves, stems, and roots of the two ecotypes of Sedum alfredii.