Miscanthus bioenergy crop stimulates nutrient-cycler bacteria and fungi in wastewater-contaminated agricultural soil

Wastewater can be recycled in agricultural soil as fertilizer to increase crop yields. However, adding wastewater induces sometimes ecotoxicological issues such as pollution by toxic compounds, which may lead to the loss of arable land. Bioenergy crops such as Miscanthus × giganteus have been tested to rehabilitate polluted soils, but the impact of Miscanthus on soil microbes is unknown. Here, we evaluated the effects of Miscanthus cropping on bacterial and fungal taxonomic composition in a wastewater-contaminated soil using synchronic and diachronic evaluation strategies. A 3-year field experiment close to Paris was set up on an agricultural site irrigated by raw wastewater for more than one century, thus resulting in strong metal and organic contamination. Soil microbial taxonomic composition was characterized by direct analysis of soil DNA using metagenomic tools such as 454 pyrosequencing of ribosomal genes. Our results demonstrate that Miscanthus cropping stimulates specific populations of bacteria such as Rhizobiales, increased by 1.4 in relative abundance, Nistrospira (x1.5), Azospira (x2), and Gemmatimonas (x2), and fungi: Glomeromycota (x3) and Mortierella (x1.5) for fungi. Noteworthy, these microbial genera are known to be strongly involved in plant symbiosis, organic matter mineralization, and nutrient cycling. Overall our findings show that Miscanthus cropping enhances regeneration of soil microbiological functions and services in polluted soil by stimulating populations beneficial for soil fertility and crop production