Rhizosphere microbial community and Zn uptake by willow (Salix purpurea L.) depend on soil sulfur concentrations in metalliferous peat soils

On numerous occasions, rhizosphere microbial activities have been identified as a key factor in metal phytoavailability to various plant species and in phytoremediation of metal-contaminated sites. For soil bioremediation efforts in heavy metal contaminated areas, microbes adapted to higher concentrations of heavy metals are required. This study was a field survey undertaken to examine rhizosphere microbial communities and biogeochemistry of soils associated with Zn accumulation by indigenous willows (Salix purpurea L.) in the naturally metalliferous peat soils located near Elba, NY. Soil and willow leaf samples were collected from seven points, at intervals 18 m apart along a willow hedgerow, on four different dates during the growing season. Soil bacterial community composition was characterized by terminal restriction fragment length polymorphism (T-RFLP) analysis and a 16S clone library was created from the rhizosphere of willows and soils containing the highest concentrations of Zn. Bacterial community composition was correlated with soil sulfate, but not with soil pH. The clone library revealed comparable phylogenetic associations to those found in other heavy metal-contaminated soils, and was dominated by affiliations within the phyla Acidobacteria (32%), and Proteobacteria (37%), and the remaining clones were associated with a wide array of phyla including Actinobacteria, Gemmatimonadetes, Planctomycetes, Verrucomicrobia, Bacteriodetes, and Cyanobacteria. Diverse microbial populations were present in both rhizosphere and bulk soils of these naturally metalliferous peat soils with community composition highly correlated to the soil sulfate cycle throughout the growing season indicative of a sulfur-oxidizing rhizosphere microbial community. Results confirm the importance of soil characterization for informing bioremediation efforts in heavy metal contaminated areas and the reciprocity that microbial communities uniquely adapted to specific conditions and heavy metals may have on an ecosystem.

► Field survey of metalliferous soil microbial communities, soil and willow chemistry.
► Spatial/temporal heterogeneity significant in microbial TRFLP, soil and willow S, Zn.
► Microbial community and willow Zn uptake were dependent on soil sulfate concentrations.
► Results challenge the paradigm that soil pH drives biogeochemistry in every soil.