Effect of decomposition products produced in the presence or absence of epigeic earthworms and minerals on soil carbon stabilization

International audienceMicrobial use efficiency is thought to greatly influence organic carbon storage in soils through the formation of decomposition products and their stabilization as organo-mineral complexes. Earthworm activity may play a significant role in these processes. Of the three ecological earthworm groups only two (endogeic and anecic species) are thought to be involved in soil organic carbon (SOC) stabilization as they are living in mineral soil. The aim of this study was to investigate the role of decomposition products produced, with and without minerals, by epigeic earthworms living at the litter-soil interphase for carbon stabilization. We investigated the impact of eight different types of decomposition products on CO2 emissions, microbial biomass, watersoluble C, mineral N and SOC pool allocation of an arenic cambisol during 79 days under laboratory conditions. Our results indicated that the nature of decomposition products affected their impact on SOC mineralization and soil physico-chemical parameters. In general, the presence of epigeic earthworms during OM decomposition decreased CO2 emissions after soil addition of decomposition products and increased microbial carbon use efficiency when compared to those produced without earthworms. Mineral-containing decomposition products increased CO2 emissions after their addition to soil when compared to their mineral free counterparts. They also changed carbon allocation to physico-chemically protected pools, decreasing the contribution of particulate organic matter when compared to mineral free decomposition products. Extrapolation of the data showed that these short-term effects were not necessarily long-term in nature, but they also indicated that microbial products produced in the presence of epigeic earthworms and minerals may increase SOC sequestration in the amended soil. We therefore conclude that the nature of decomposition products is crucial for their fate in soil and that in contrast to the general paradigm, epigeic earthworms could have an important role to play in SOC sequestration through the formation of material susceptible to be protected, when incorporated into mineral soil