High-throughput assessment of bacterial communities in riparian soils designed for decontamination of anthropogenic nitrogen

Riparian buffer strips are used to protect aquatic ecosystems from the input of anthropogenic nitrogen. This effect is linked to several factors, including plant uptake, soil properties and the presence and activity of denitrifying microorganisms residing both in soil and in the rhizosphere of the plants [1, 2]. Aim of this work was to assess the total bacterial community of riparian strips soil, and to identify any significant correlation between bacterial populations, treatments and soil chemical properties. A total of twenty samples from buffer and external areas were sampled at three different depths (surface 0-15 cm, medium 45-60 cm and deep 80-100 cm) in two different seasons (spring and autumn). DNA was amplified with tagged primers targeting the V3-V4 region of 16S rRNA and sequenced with Illumina MiSeq operating in 300 bp X2 paired-reads module. Sequences processing resulted in 2.5 millions high quality sequences, which were reduced to 74632 in each of the 20 samples in order to avoid biases related with the analyses of samples with differing sizes. Good’s coverage values were ≥ 99.9% for all samples, thus showing that the sequencing effort was enough to capture the vast majority of bacterial diversity. Dominating phyla were Acidobacteria, Chloroflexi and Proteobacteria, followed by Firmicutes, Bacteroidetes, Nitrospirae and Verrucomicrobia. Multivariate analyses on OTUs abundances identified a number of significant differences related to the soil type (control or buffer strip) and to the depth. A number of OTUs showed significant correlations with organic carbon and potential nitrification data, while Spearman correlation analyses identified inverse significant correlations between organic carbon, in situ denitrification and bacterial richness. Additional analyses are undergoing to better assess further interactions between Illumina high- throughput sequences and chemical data.