Organic agriculture and hedgerows uphold endospheric wheat microbiota at field and landscape scale. Landscape scale impact on the wheat root endospheric microbiota composition

Agricultural intensification has been demonstrated to induce a loss of biodiversity in agroecosystems. Though, its impact on microorganisms was overlooked, despite the key role of symbiotic microorganisms in plant nutrition and protection. Organic agriculture and semi-natural elements constituting the field edges may promote a higher diversity in microorganisms thanks to lower anthropic and chemical disturbance and their beneficial role in promoting plant diversity. These effects might be seen at the local and the landscape scales. Thanks to a large-scale experimental design encompassing a nested-spatial scale sampling, we sampled wheat individuals in pairs of wheat fields (one conducted in organic and one in conventional farming) along a gradient of distance to the edges (two edge types : hedgerow versus grassy), in 20 landscapes selected along an uncorrelated gradient of organic farming and hedgerows density. Using a mass-sequencing approach, we demonstrated in most phyla a higher richness in organic fields and near to the field edge at the field scale in fungi and a higher bacteria richness in fields surrounded with a high cover percentage of organic farming at the landscape scale. Except Basidiomycota, fungi did not respond to hedgerow presence or density in the landscape while hedgerows density in the landscape was negatively related with total bacterial richness but induced contrasted responses at the phylum level. Organic agriculture and field edges can be seen as refuges of microorganisms at field and landscape scale. This work highlighted the importance of agricultural management on microorganisms at larger spatial scales than the only field scale. Organic farming in the landscape might contribute to a rescue effect of the field microbial assemblage even if conducted in conventional agriculture.