Determinants of the distribution of nitrogen-cycling microbial communities at the landscape-scale

Little information is available regarding the landscape-scale distribution of microbial communities and its environmental determinants. However, a landscape perspective is needed to understand the relative importance of local and regional factors and land management for the microbial communities. In this manuscript, we investigated the distribution of functional microbial communities involved in N-cycling and of the total bacterial and crenarchaeal communities over 107 sites using a grid with a 16 km lag distance within Burgundy, a 31 500 km2 region in France. After quantifying the abundances of the total bacterial, crenarchaeal, nitrate-reducing, denitrifying and ammonia-oxidizing communities and measuring 42 soil physico-chemical properties at each sampling site, we used by canonical variation partitioning to determine the relative contributions of land use, spatial distance, climatic conditions, time and soil physico-chemical properties to the distribution of the different communities. Although many environmental variables were significant predictors, only a few accounted to a large amount of the total variance in the distribution of the studied microbial guilds. Altogether we could explain up to 85 % of the spatial variation in community abundances with soil chemical properties as the main driver. We found spatial correlation up to 140 km and geostatistical modelling was used to generate predictive maps of the distribution of microbial communities across the 31 500 km2 Burgundy region. The present study, which is the most comprehensive spatially explicit analysis of patterns of microbial communities to date, highlights the potential of such approach for microbial ecology to identify the overarching factors driving the spatial heterogeneity of microbial communities even at the landscape scale. It also provides the first maps of the distribution of microbial guilds at a scale which is of relevance for policy makers and stakeholders for ecosystem management.