Abstract
Phytoextraction is influenced by the indigenous soil microbial communities during the remediation of heavy metal contaminated soils. Soil microbial communities can affect plant growth, metal availability and the performance of phytoextraction-assisting inocula. Understanding the basic ecology of indigenous soil communities associated with the phytoextraction process, including the interplay between selective pressures upon the communities, is an important step towards phytoextraction optimization. This study investigated the impact of cadmium (Cd), and the presence of a Cd-accumulating plant, Carpobrotus rossii (Haw.) Schwantes, on the structure of soil-bacterial and fungal communities using automated ribosomal intergenic spacer analysis (ARISA) and quantitative PCR (qPCR). Whilst Cd had no detectable influence upon fungal communities, bacterial communities underwent significant structural changes with no reduction in 16S rRNA copy number. The presence of C. rossii influenced the structure of all communities and increased ITS copy number. Suites of operational taxonomic units (OTUs) changed in abundance in response to either Cd or C. rossii, however we found little evidence to suggest that the two selective pressures were acting synergistically. The Cd-induced turnover in bacterial OTUs suggests that Cd alters competition dynamics within the community. Further work to understand how competition is altered could provide a deeper understanding of the microbiome-plant-environment and aid phytoextraction optimization.
Highlights
Phytoextraction is influenced by the indigenous soil microbial communities during the remediation of heavy metal contaminated soils
Despite the high cadmium (Cd) doses used in this experiment, we observed no significant change in the biomass of plant shoots
Irrespective of Cd treatments, there was a significant difference in the copy number of the fungal internal transcribed spacer (ITS) between bulk and rhizosphere communities in weeks 1 (F(1,24) = 7.36, p < 0.05) and 8 (F(1,24) = 8.39, p < 0.01) as determined by factorial ANOVAs of quantitative PCR (qPCR) data (Fig. 1A)
Summary
Phytoextraction is influenced by the indigenous soil microbial communities during the remediation of heavy metal contaminated soils. Indigenous soil- and rhizosphere-microbial communities are a significant in situ variable with the potential to inhibit or out-compete phytoextraction-assisting inocula[16]. The importance of indigenous microbial communities in metal accumulation was highlighted by microcosm studies which reported that disturbance (gamma-irradiation) of native soil communities significantly reduced Cd- and Zn-accumulation by Arabidopsis halleri, even though plant biomass was unaffected[17]. Investigations that seek to understand changes to the in situ microbial community during phytoextraction could provide a deeper understanding of the microbiome-plant-environment[18]. Studies that tracked the rhizosphere communities of Sedum plumbizincicola in Cd contaminated soil found that the indigenous community was significantly altered following inoculation with a single plant-growth-promoting bacterium[13]. The changes to the community, which remained even when the initial inoculum was no longer detectable, included decreased diversity and the enrichment of indigenous plant-growth-promoting (PGP)-rhizosphere bacteria
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