The aim of this thesis is to identify and to specify biotic and abiotic processes affecting the Ca behavior and specifically the Ca isotope fractionation at the geosphere/biosphere/hydrosphere interface by combining different experimental studies (hydroponic and microcosm).Results of hydroponic experiments allow to identify three Ca isotopic fractionation levels, which are driven by physico-chemical mechanisms and enrich the plant organs in the light 40Ca isotope. Moreover, the evolution of Ca isotopic composition of nutrient solution and plants follow an equilibrium law (αplants/nutrient solution = 0.99858).Abiotic column experiments show no Ca isotopic fractonation during apatite disolution, whatever the nature of the acid (mineral or organic). At the opposite, during biotic microcosm experiments, only the combined action of roots of scots pines and bacteria on apatite substratum enrich the percolate solution in heavy 44Ca of 0.22‰.
