Mapping and determinism of soil microbial community distribution across an agricultural landscape

Despite the relevance of landscape, regarding the spatial patterning of microbial communities and the relative influence of environmental parameters vs human activities, few investigations have been conducted at this scale. We used a 215 m x 215 m systematic grid to characterize the distribution of soil microbial communities at 278 sites across a monitored agricultural landscape of 13 km². Molecular microbial biomass was estimated by soil DNA recovery and bacterial diversity by 16S rRNA gene pyrosequencing. Geostatistics provided the first maps of microbial community at this scale and revealed a heterogeneous but spatially-structured distribution of microbial biomass and diversity with patches of several hundreds of meters. Variance partitioning revealed that soil and land-use characteristics explained 55 to 78% of the microbial abundance and diversity distribution. Microbial biomass and bacterial richness distributions were mainly explained by soil pH and texture whereas bacterial evenness distribution was mainly related to land-management. Bacterial diversity (richness, evenness and Shannon index) was positively influenced by cropping intensity and especially by soil tillage, resulting in spots of low microbial diversity in soils under forest management. Spatial descriptors also explained a small but significant portion of the microbial distribution suggesting that landscape configuration influences the shaping of microbial biomass and bacterial diversity.