Turnover of soil microbial diversity is driven by wide-scale environmental heterogeneity

Spatial scaling and determinism of the wide-scale distribution of macroorganisms’ diversity has been largely demonstrated over a century. For microorganisms, this fundamental question requires more thorough investigation. Here, we investigate the spatial structuration of soil microbial communities on a wide scale, particularly bacteria and fungi, and focus on both processes and filters shaping their abundance and diversity. Soil bacterial and fungal communities were characterized on the largest spatially explicit soil sampling available in France (2,085 soils over ca. 5.3 105 km2) by using molecular techniques (biomass, fingerprinting and pyrosequencing of ribosomal genes). With this framework, we provide an extensive map of soil molecular microbial biomass, revealing its structuration into non-random spatial patterns determined by local factors (soil pH, organic carbon, texture, and land use) rather than by global filters (e.g. climate). By applying the taxa-area relationship and developing an innovative evaluation of the habitat-area relationship, we show that the turnover rate of bacterial diversity in soils on a wide scale is highly significant and strongly correlated with the turnover rate of soil habitat. This result highlights the importance of environmental selection in shaping soil microbial diversity. In addition, by simulating new landscape configurations, we suggest that dispersal of soil microbes may be limited, in agreement with Hubbell’s Neutral Theory. Variance partitioning approaches allowed the identification of the environmental filters shaping both bacterial and fungal diversity: pH, trophic resources (organic carbon, nitrogen and C:N ratio), texture and land use; and of the scales at which dispersal was limited: coarse (80 - 110 km) and medium (40 - 60 km) spatial scales. Applying next generation sequencing techniques on this framework supports these results and show that soil microbial diversity turnover is much higher than suggested in previous studies. Consequently, as the diversity of micro- and macroorganisms appears to be driven by similar processes (dispersal and selection), maintaining diverse and spatially structured habitats is essential for soil biological patrimony and the resulting ecosystem services.