Unique Rhizosphere Micro-characteristics Facilitate Phytoextraction of Multiple Metals in Soil by the Hyperaccumulating Plant Sedum alfredii

Abstract

Understanding the strategies that the roots of hyperaccumulating plants use to extract heavy metals from soils is important for optimizing phytoremediation. The rhizosphere characteristics of Sedum alfredii, a hyperaccumulator, were investigated 6 months after it had been planted in weathered field soils contaminated with 5.8 μg of Cd g, 1985.1 μg of Zn g, 667.5 μg of Pb g, and 698.8 μg of Cu g. In contrast with the non-hyperaccumulating ecotype (NHE), the hyperaccumulating ecotype (HE) of S. alfredii was more tolerant to the metals, and higher levels of Cd and Zn accumulated. The HE was characterized by a unique rhizosphere, including extensive root systems, a reduced soil pH, a higher metal bioavailability, and increased rhizomicrobial activity. The bioavailability of metals was significantly correlated with the HE's unique bacterial communities (P < 0.005). The HE harbored abundant Streptomyces (9.43%, family Streptomycetaceae), Kribbella (1.08%, family Nocardioidaceae), and an unclassified genus (1.09%, family Nocardioidaceae) in its rhizosphere, a composition that differed from that of the NHE. PICRUSt analysis predicted high relative abundances of imputed functional profiles in the HE rhizosphere related to membrane transport and amino acid metabolism. This study reveals the rhizosphere characteristics, particularly the unique bacterial rhizobiome of a hyperaccumulator, that might provide a new approach to facilitating heavy metal phytoextraction.

Cadmium Exposure-Sedum alfredii Planting Interactions Shape the Bacterial Community in the Hyperaccumulator Plant Rhizosphere

“…The actinobacterial genus Streptomyces was responsible for the majority of divergence among the rhizospheres of HE S. alfredii and bulk soils, contrasting with the rhizosphere of NHE S. alfredii. Our previous study also found HE harbored abundant Streptomyces in its rhizosphere during the phytoremediation of multimetalcontaminated soil (25). Streptomyces is the largest antibiotic-producing genus in the microbial world (49).…”

“…However, little knowledge is available regarding the basic ecology of indigenous soil microbial communities associated with the phytoextraction process in polluted soils by this plant species. Although our recent study indicated that the rhizosphere microcharacteristics, including the bacterial community, facilitate phytoextraction of multiple metals in soil by S. alfredii (25), the relationships between the bacterial rhizobiome and the influencing factors or variables, such as soil type, pollutant species, and pollution levels, are still unknown. Therefore, the present study investigated the characteristics of the rhizosphere bacterial community of the hyperaccumulator S. alfredii under different Cd treatments and the interaction of Cd presence and roots of S. alfredii on the structure of soil bacterial communities, using 16S rRNA gene amplicon sequencing.…”

Variation of the Bacterial Community in the Rhizoplane Iron Plaque of the Wetland Plant Typha latifolia

“…According to Figure 3 and Table 1, it can be speculated that the higher abundances of functional genes in the I of either soil are attributed to the special environment of the root surface that was more affected by the root radial oxygen loss and the physicochemical properties of the soils. Similarly, Hou et at predicted the functional genes of the bacterial communities in the rhizosphere of Sedum alfredii , a hyperaccumulator, and proposed that the compositional difference of predicted functional genes was a consequence of the special environment of the rhizosphere, which was severely polluted by heavy metals in their case [21]. Although PICRUSt is useful for supplementing 16S rRNA analyses in metagenome studies, it might lead to confusion when analyzing microbial communities that have a large proportion of poorly characterized populations [21].…”

Rhizosphere Soil Microbial Properties on Tetraena mongolica in the Arid and Semi-Arid Regions, China

“…Soil microbial richness and activity are closely related to the availability of soil nutrients. “Amino Acid Metabolism” were the energy and carbon sources of bacterial metabolism [ 44 ]. Thus, rhizosphere soil could promote more amino acid production and humic substance synthesis.…”