Microbial community dynamics in the rhizosphere of a cadmium hyper-accumulator

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.

Bacterial and fungal communities are differentially modified by melatonin in agricultural soils under abiotic stress

“…Controls involved dilute ethanol replacing melatonin (see below) and/or sterile Milli-Q water replacing cadmium. These concentrations were selected to be within the range of those reported to induce effects on soil microbial activities in previous studies for cadmium (Cáliz et al, 2013, Wood et al, 2016) and salt (Rath et al, 2016). Based upon preliminary studies, soils were treated to 80-90% field capacity, to ensure all soils were sufficiently exposed to stressor and melatonin.…”

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

“…The rhizosphere habitat is affected by spatial and temporal variations in soil properties and the physiological state of the plant (12). Heavy metals in soils could alter the structure of soil microbial communities (13). Previous studies found that presence of heavy metals, including Cd, in soils decreased the microbial biomass and resulted in a shift in the microbial community structure (14)(15)(16).…”

“…Previous studies found that presence of heavy metals, including Cd, in soils decreased the microbial biomass and resulted in a shift in the microbial community structure (14)(15)(16). On the other hand, heavy metals in soils could increase the prevalence of specific heavy metal-resistant bacteria (13). Although a considerable amount of metalresistant bacteria from the rhizosphere of hyperaccumulators have been isolated using traditional culture-dependent techniques, the microbial assemblages associated with hyperaccumulation remain poorly understood (5,17).…”

“…Although a considerable amount of metalresistant bacteria from the rhizosphere of hyperaccumulators have been isolated using traditional culture-dependent techniques, the microbial assemblages associated with hyperaccumulation remain poorly understood (5,17). Furthermore, previous research tended to focus on the important effect of a single microbial inoculum on the enhancement of phytoextraction but overlooked the complexity of the plant-soil environment in which a variable indigenous microbial community may outcompete or inhibit phytoremediation-assisting inocula (13,18).…”

Plant species and soil type influence rhizosphere bacterial composition and seedling establishment on serpentine soils

“…On the other hand, soil physical 63 and chemical properties can also be strong drivers of rhizosphere and rhizoplane microbial 64 community composition, particularly on large scales or across soils that vary widely in 65 composition. For example, pH (Bartram et al 2014;Wu et al 2017), salinity (Sardinha et al 2003; 66 Dillon et al 2013), drought (Barnard, Osborne and Firestone 2013; Chodak et al 2015), and the 67 presence of heavy metals (Wood et al 2016) all influence soil and root-associated microbial 68 community structure. Still, the relative importance of plant identity and soil chemistry across soil 69 gradients remains difficult to predict in large part because plant species are often restricted to 70 particular soil types.…”