Earthworms and plant growth: novel mechanisms and their implications

International audienceEarthworms are responsible for many physical, chemical, biochemical and ecological modifications of soils. These modifications have consequences for plant growth and development. However, despite a well established positive effect of earthworms on plant growth, the identification of soil modifications responsible for this positive effect is still problematic as these modifications often occur simultaneously. In our laboratory, we tested several mechanisms independantly; we found that the effect of earthworms on water availability for the plant, on nitrogen release, or parasite biocontrol were not sufficient to explain alone the positive effect o plant growth. The emission of signal molecules affecting plant growth, development or immunity seems to be a necessary mechanism to understand this effect. I will propose a new hypothesis on the coupling between nutrient release and emission of signal molecules, which could explain the synchronization between the kinetics of organic matter mineralization and nutrient uptake by the plant. Preliminary results about the effect of earthworm casts on plant growth and development in split-root systems, about the quantification of microorganisms involved in the nitrogen cycle as well as about a mathematical model of signal molecule diffusion support this hypothesis. Some elements suggest that this coupling hypothesis could eventually be generalized to the effect of other soil organisms on plant growth