Positive effect of the Miscanthus bioenergy crop on microbial diversity in wastewater-contaminated soil

In France, about 90,000 ha per year of arable land become unsuitable for food production due to erosion, acidification, sealing and pollution by metallic and organic compounds. Bioenergy crops such as Miscanthus x giganteus are used to rehabilitate polluted soils for crop production. Although the economic potential of this crop is known, the crop abilities to regenerate the soil biological properties enabling sustainable crop production still remain unclear. Here, we evaluated the effects of the Miscanthus crop on the abundance and diversity of soil bacterial and fungal communities in a wastewater-contaminated soil, using synchronic and diachronic evaluation strategies. A 3-year field experiment, near Paris, was set up on an agricultural field irrigated with raw wastewater for more than 100 years, thus inducing a strong metal and organic contamination of the soil. We characterized the abundance and diversity of soil microbial communities using metagenomic techniques. Our results show that the Miscanthus crop had an early effect on microbial communities by stimulating bacterial diversity, by about 20 %, and fungal diversity, by about 10 %. This positive effect could be explained by the release of fresh organic matter from litter decomposition and root exudation, and by the absence of tillage and pesticide spraying, which are known to degrade soil microflora. On the other hand, no significant effect on microbial biomass has been recorded. Overall our findings show that Miscanthus cropping is a promising practice to enhance the regeneration of soil microbiological diversity and to reclame polluted soils.