CONICET | Buscador de Institutos y Recursos Humanos

Introduction Previous studies focusing on local diversity were unable to grasp any deleterious effects of monocropping on soil bacterial communities. In opposition, variation of beta-diversity at a regional scale can provide insights into the importance of habitat conditions in structuring the communities. Objectives The aim of this work was to uncover the response of soil bacterial communities in no-till production fields to monocropping in comparison to high crop rotation. Methods Blocks of treatments were sampled at 4 different locations across a scale of 400 km along 3 successive cropping seasons. In each location we sampled a natural field (grassland) and two production fields managed under no-till according to the following standards: 1) Crop rotations and appropriate nutrient amendment, 2) Soybean monoculture and minimal nutrient inputs. Three replicates from the top 10 cm of bulk soil separated 50 m from each other were taken for each treatment, site and time, making a total of 108 samples. The Mothur and QIIME pipelines were used to process and analyze the reads of the bar-coded 454 sequencing of the V4 region of the 16S rRNA. A total of 333180 OTUs averaging 254 bp were used for analysis. Results There were no significant data differences in α-diversity related to sites or soil management. However, histograms of pairwise distancesbetween all pairs of samples within treatments (weighted Unifrac, Fig 1) revealed that β-diversity was reduced and had narrower breadth in monocropping agriculture than in grassland soils while fields under crop rotations was in between. At the phylum level the magnitude of this effect depended on the richness of each taxon at the regional scale. Conclusions Crop monoculture would drive the homogenization of bulk soil bacterial communities across a regional scale. Variation in taxa responses to agricultural management could be explained by differences in gamma diversity.