Effect of inorganic nitrogen fertilizers application on bacterial and archaeal community structures of durum wheat

Because nitrogen (N) is a limiting nutrient to plants in most natural ecosystems, N fertilization has become an important agricultural practice. In this study, we examined the durum wheat bacterial and archaeal community structure and diversity of different soils: soils treated with inorganic nitrogen fertilizers collected in March (rhizosphere) and September (bulk soil), soils not fertilised sampled in March (rhizosphere), and an uncultured soil also sampled in March (bulk soil). Illumina 16S rRNA gene amplicon sequencing followed by bioinformatic and statistical analyses was performed. Inorganic nitrogen application affected the structure and diversity of wheat-associated bacterial and archaeal communities, as well as 16S rRNA gene-predicted functional structure and soil properties, such as pH which was significantly correlated to the relative abundances of several genera. IndVal analysis was used to identify key microbial taxa affected by changes in the soil environment. Microbial taxa related to different processes of the N-cycle, such as Candidatus Nitrososphaera, were indicators of inorganic N-fertilization as well as not fertilized samples. The application of inorganic nitrogen fertilizers negatively affected bacterial richness and diversity, but significantly increased the relative abundance of both oligotrophic, such as the Acidobacteria, and copiotrophic bacteria, such as the Alphaproteobacteria in the samples taken in March. Not fertilized samples showed higher relative abundances of Planctomycetes and Bacteroidetes. In conclusion, our results highlight the impact of inorganic nitrogen fertilization on durum wheat microbial community structure and diversity, as well as the relevance of soil pH as the main deterministic abiotic factor for soil microbial community structure.