Fate of crop residues incorporated in soil: towards linking microbial diversity and evolution of organic matter

Among the microbial functions involved in biogeochemical cycles, those related to carbon cycle play a central role in the biological functioning of agro-ecosystems, in particular because of their involvement in soil fertility, environment quality and global changes. In spite of its major role in organic matter degradation processes, the microbial component involved is poorly documented, particularly in terms of populations and functions, and then considered as a “functional black box”. In this context, our objective was to progress in our knowledge of the microbial populations responsible for organic matter degradation in soil. Crop residues represent one of the most important hot spots (zones of increased biological activity) and ecological niches to study microbes involved in organic matter degradation. Our objective was to characterize, in a field experiment, the dynamics of the microbial communities in the detritusphere (zone of the soil under the influence of crop residues) in relation to the biochemical quality of the residue and the evolution of the soil organic matter. For this, residues from different plant types: wheat, colza, and alfalfa were incorporated separately in different plots. From the incorporation date, soils were sample each 1 month for 1 year. The responses of microbial communities to residue supply have been assessed by using molecular methods allowing the characterization of the diversity of microorganisms (DNA fingerprinting, clone libraries). In parallel, the dynamics of the biochemical quality of the residues have been monitored (Near Infra Red Spectrometry).Results showed a strong influence of residue biochemical quality on the dynamics of microbial communities. Furthermore, most of the microbial modifications occurred in the close neighbourhood of the residue, highlighting the particular ecological significance of the detritusphere. Coupling of microbial data and organic mater biochemical data allowed linking the dynamics of microbial communities with the fate of organic matter in soil.