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Unique rhizosphere micro-characteristics facilitate phytoextraction of multiple metals in soil by the hyperaccumulating plant Sedum alfredii Dandi Hou, Kai Wang, Ting Liu, Haixin Wang, Zhi Lin, Jie Qian, Lingli Lu, and Shengke Tian Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 24 Apr 2017 Downloaded from http://pubs.acs.org on April 24, 2017
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Environmental Science & Technology
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TITLE: Unique rhizosphere microcharacteristics facilitate phytoextraction of multiple metals in soil by the hyperaccumulating plant Sedum alfredii
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Dandi Hou1, Kai Wang2, Ting Liu1, Haixin Wang1, Zhi Lin1, Jie Qian2, Lingli Lu1, and
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Shengke Tian1*
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Author affiliations and addresses:
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1
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of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058,
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China
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2
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Corresponding author:
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Shengke Tian
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MOE Key Laboratory of Environmental Remediation and Ecological Health, College
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of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058,
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China. E-mail:
[email protected]. Tel: +86-571-88982515. Fax: +86-571-88982907.
MOE Key Laboratory of Environmental Remediation and Ecological Health, College
School of Marine Sciences, Ningbo University, Ningbo, 315211, China
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ACS Paragon Plus Environment
Environmental Science & Technology
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Abstract
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Understanding the strategies that the roots of hyperaccumulating plants use to extract
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heavy metals from soils is important for optimizing phytoremediation. The
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rhizosphere characteristics of Sedum alfredii, a hyperaccumulator, were investigated 6
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months after planting in weathered field soils contaminated with 5.8 µg·g-1 Cd,
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1985.1 µg·g-1 Zn, 667.5 µg·g-1 Pb, and 698.8 µg·g-1 Cu. In contrast with the non-
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hyperaccumulating ecotype (NHE), the hyperaccumulating ecotype (HE) of S. alfredii
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was more tolerant to the metals and accumulated higher levels of Cd and Zn. The HE
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was characterized by a unique rhizosphere including extensive root systems, reduced
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soil pH, higher metal bioavailability, and increased rhizomicrobial activity. The
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bioavailability of metals was significantly correlated with the HE’s unique bacterial
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communities (P97% sequence
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identity threshold, which yielded 17,101 bacterial operational taxonomic units
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(OTUs). A total of 8,701 OTUs were obtained after randomly resampling Illumina
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16S sequence reads to the same depth (28,100 sequences per sample). The five most
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abundant OTUs across all soil samples were Proteobacteria (27.3%), Chloroflexi
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(25.9%), Actinobacteria (16.1%), Acidobacteria (13.1%), and Bacteroidetes (7.7%),
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which potentially represent the core microbiome of the heavy metal-contaminated
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paddy soil. These microorganisms, especially Proteobacteria, Actinobacteria, and
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Acidobacteria, have been identified as the most dominant phyla in heavy metal
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contaminated soils.44, 45 Thus, the presence of these phyla may provide a stabilizing
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element in heavy metal contaminated soils, as previously reported.46, 47
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Environmental Science & Technology
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Plant-driven
changes in
rhizospheric microbial communities are
well-
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documented.14 Reductions in bacterial community diversity in rhizosphere soils have
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been observed in some plant systems.14,
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communities was compared between the rhizospheric and bulk zones of HE and NHE
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S. alfredii. Although no difference in either bacterial richness estimators (Chao1 and
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Sobs) or diversity indexes (Shannon and Simpson) was noted (Table S1), there were
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significant differences in overall community structure between the rhizosphere and
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bulk soils for both HE and NHE S. alfredii (Fig. 3). PCoAs revealed that the
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rhizocompartments separated across the first principal coordinate (Fig. 3A and Fig.
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S4), indicating that the largest source of variation in root-associated microbial
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communities is proximity to the roots. PERMANOVA corroborated the finding that
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rhizospheric compartmentalization comprises the largest source of variation (25.6%,
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P
