Rhizosphere characteristics of the hyperaccumulator plant Sedum alfredii in phytoremediation of multi-metal contaminated soil. soil metagenome

Understanding the strategies that roots of hyperaccumulators utilize to extract heavy metals from soils is important for optimizing phytoremediation of contaminated sites. Rhizosphere characteristics of a hyperaccumulator plant species, Sedum alfredii, were investigated when planted in soils contaminated with Cd, Pb, Zn, and Cu. In contrast with its non-hyperaccumulating ecotype (NHE), the hyperaccumulating ecotype (HE) of S. alfredii showed an extrodinary capacity to tolerate and extract the heavy metals in the contaminated soils, as well as very specific rhizobacterial properties. The HE rhizosphere was characterized by extensive root systems and drastically lower soil pH. Enhanced microbial activities, indicated by high microbial biomass carbon and metabolic enzymes, were also noted in the rhizosphere soil with plantation of HE, but not the NHE. The 16S rRNA sequencing of the rhizosphere and bulk soils suggested that HE was characterized by distinct rhizobacterial communities, and harbored abundant Actinomycetales, Cytophagia, Solibacterales, and Roseiflexales, which may contribute to metal activation and uptake. This study revealed the rhizosphere ecology of HE S. alfredii during phytoremediation of polluted soils, suggesting that efficacy of contaminants extraction by the plants may be associated with its extensive root growth, soil acidification, and enhanced rhizomicrobial activities by specific bacterial communities.

阐明超富集植物（hyperaccumulator）根系从土壤中提取重金属的策略，对于优化污染场地的植物修复具有重要意义。本研究针对种植于镉（Cd）、铅（Pb）、锌（Zn）与铜（Cu）复合污染土壤中的超富集植物东南景天（Sedum alfredii）的根际特征展开了系统调查。与该物种的非超富集生态型（non-hyperaccumulating ecotype, NHE）相比，东南景天的超富集生态型（hyperaccumulating ecotype, HE）不仅展现出极强的重金属耐受与提取能力，同时具备独特的根际细菌群落特性。超富集生态型的根际以发达的根系体系与显著降低的土壤pH值为典型特征；在种植超富集生态型的根际土壤中，还可观测到以高微生物生物量碳与代谢酶活性为指示的微生物活性增强现象，而非超富集生态型则未出现该特征。通过对根际土与非根际土的16S rRNA测序（16S rRNA sequencing）分析发现，超富集生态型拥有独特的根际细菌群落结构，其根际中富集有放线菌目（Actinomycetales）、噬纤维菌纲（Cytophagia）、溶杆菌目（Solibacterales）与红弯线菌目（Roseiflexales），上述类群可能参与重金属的活化与植物吸收过程。本研究阐明了东南景天超富集生态型在污染土壤植物修复过程中的根际生态机制，结果表明植物对污染物的提取效率与其发达的根系生长、土壤酸化作用，以及特定细菌群落介导的根际微生物活性增强密切相关。