Soil pH dominance over livestock management in determining bacterial assemblages through a latitudinal gradient of European meadows and pastures

Grasslands represent key functional ecosystems due to their global contribution to macronutrients cycling, and as reservoirs of microbial diversity. The strategic importance of these habitats rests on their involvement in carbon and nitrogen fluxes from atmosphere to soil, while at the same time offering extensive sites for livestock rearing. The management type, distinguishing the pasture or meadow land use, was investigated as a variable for its possible effects on overall bacterial diversity and on specific genes linked to functional guilds. Its contribution was compared to that of other variables as region, soil pH and soil organic carbon in order to rank their respective hierarchies in shaping microbial community structure. A latitudinal transect across the European continent was studied with three sampling clusters located in Norway, France and Northern Italy. Methods involved 16S DNA metabarcoding and quantitative PCR for bacterial and archaeal nitrification, intermediate or terminal denitrification, and nitrogen fixation genetic determinants. Results outlined that soil pH exerted the dominant role, affecting high taxonomy ranks and functions, along with organic carbon and region, with whom it partly co-varied. On the contrary, the management type showed its effects mostly at deeper taxonomical resolution as the OTU level and had no significant influence on the quantitative counts of functional genes. This suggests an ecological equivalence between the impacts of pasture and meadow practices, which are both perturbations sharing the aspect of vegetation withdrawal by browsing or cutting respectively.