Ecological corridors homogenize plant root endospheric mycobiota.

Ecological corridors promote species coexistence in fragmented habitats where dispersal limits species fluxes. The corridor concept was developed and investigated with macroorganisms in mind, while microorganisms, the invisible majority of biodiversity, were disregarded. We analyzed the effect of corridors on the dynamics of endospheric fungal assemblages associated with plant roots at the scale of 1 m over 2 years (i.e. at five time points) by combining an experimental corridor-mesocosm with high-throughput amplicon sequencing. We showed that plant root endospheric mycobiota were sensitive to corridor effects when the corridors were set up at a small spatial scale. The endospheric mycobiota of connected plants had higher species richness, lower beta-diversity, and more deterministic assembly than the mycobiota of isolated plants. These effects became more pronounced with the development of host plants. Biotic corridors composed of host plants may thus play a key role in the spatial dynamics of microbial communities and may influence microbial diversity and related ecological functions.

Organic agriculture and field edges uphold endospheric wheat microbiota at field and landscape scale.

Agricultural intensification has been demonstrated to induce a loss of biodiversity. Despite the key role of symbiotic microorganisms in plant nutrition and protection, the impact of agricultural intensification on these microorganisms is not fully understood. Organic farming and field edges (as semi-natural elements) may promote a higher microbial diversity thanks to lower anthropic disturbance and higher plant diversity. We sampled wheat individuals in pairs of wheat fields (one organic and one conventional) along a distance gradient to the edges (hedgerow vs. grassy), in 20 landscape windows selected along an uncorrelated gradient of organic farming and hedgerow density. We demonstrated that organic farming shaped microbial composition and increased fungal and bacterial richness, while hedgerows had a neutral or negative effect on richness depending on the microbial phyla considered. In contrast to bacteria, fungal communities were heterogeneously distributed within fields, having a higher diversity for some phyla close to field edges. Overall we highlighted that fungi responded more to the field scale while bacteria were more affected by landscape scale. The effect of agricultural intensification on plant microbiota and therefore on the functions provided by microorganisms to the plants has to be considered at a multiple spatial scale-from field to landscape.