Dynamics of microbial communities over the growing season in two contrasted tillage regimes. SOLRES454

It is well recognized that agricultural productivity strongly relies on a wide range of ecosystem services provided by the soil biota. Although plowing is one of the main components of conventional, long-term detrimental effects such as soil erosion and loss of soil organic matter have been recognized. Consequently, moving towards more sustainable agricultural management is not without consequences for the soil microbiota in terms of structure and function. In addition, the root establishment over the growing season may moderate the soil treatment effect on the soil microbiota. Here, we used amplicon-based sequencing (Illumina) to explore the response of the soil microbial community structure over the growing season of two crops: Vicia faba and Triticum aestivum in two contrasted tillage regimes: conventional (CT) and reduced tillage (RT). We reported a substantial shift in community structure between CT and RT, whereas the influence of the growing season on the tillage effect was very slight when compared to the tillage effect. After 6 years of conversion from CT to RT, lower nutrient and moisture and higher compaction were reported in RT leading to identify microbial communities at high-taxonomic level associated with different lifestyles (e.g. copiotrophic vs. oligotrophic, symbionts) and feeding type. Although the diversity at all phylogenetic levels is relevant for the functioning of a microbial community, and finally for the entire ecosystem functioning, describing the entire diversity of microbial communities with respect to the change in environmental factors remains a challenge by far as we have little or no information regarding the ecological attributes of many microbial taxa and many OTUs cannot be assigned at lower taxonomic levels.