Shaping of soil microbial communities by plants does not translate into specific legacy effects on organic carbon mineralization

International audiencePlants shape soil microbial communities through their root architecture, their rhizodeposits and return of dead plant material to the soil. These interactions can have a strong influence on the soil organic carbon dynamics. However, it is unclear whether the plant species effects on the soil microbial community could influence the organic carbon mineralization through plant legacy effects. Therefore, we examined how and to what extent a short-term plant growing phase affected the total and active soil microorganisms and through a possible plant legacy, also the mineralization of soil organic carbon, a central ecosystem function. Using a controlled pot experiment, we first showed that the two phylogenetically distinct plants, Arabidopsis thaliana and Triticum aestivum, differently shaped the soil microbial communities when recruiting from the same soil community. Although both plants recruited plant-growth promoting bacteria in the vicinity of their roots, A. thaliana had a stronger effect than T. aestivum and also recruited saprophytic fungi, while inhibiting fungal pathogens. Due to plant legacy effects on the soil microbial communities, different microbial successions occurred in the two previously planted soils when subjected to plant litter. By contrast, plant legacy effects on soil basal respiration were not plant-specific, with basal respiration increasing similarly in both cases and moreover did not translate to changes in litter carbon mineralization in the short-term of 49 days. Our results suggest that the soil nutrient dynamics rather than changes in soil microbial community composition drive the organic carbon mineralization of added litter. The present study brings new insights in how the relationships between plants, microorganisms and soil nutrient dynamics affect litter carbon cycling