Plant activity in the rhizosphere can alter the decomposition of native soil organic matter (SOM). The mechanisms behind this so-called rhizosphere priming and how plants can control this process are still unclear. We monitored plant-soil carbon (C) fluxes during the first ten weeks of rhizosphere development. We grew poplars from stem cuttings in forest soil within climate chambers under continuous 13C-CO2 labelling. Photosynthetic C assimilation and respiratory C release were continuously measured. In this study we did not observe a plant-C input quantity related priming along with rhizosphere development, but we detected an unexpected temporary priming during the first 3-5 weeks of rhizosphere development. We hypothesize that the underlying mechanism of this priming was the release of specific compounds to enhance SOM mineralisation by the plant in response to stress condition (nutrient limitation). This hypothesis is based on several evidences: (1) the amount of primed C was larger than microbial biomass C, (2) the plants were strongly limited in their growth and showed leaf chlorosis indicating nutrient deficiency, most probably caused by reduced reserves in the stem cuttings after long-term storage (7.5 months) and (3) the most growth-limited plants with the smallest leaf areas featured the highest increase in the proportion of assimilated C detected in the soil respiration, which occurred in parallel to the SOM priming. Our results give evidence for a not intensively discussed potential mechanism of rhizosphere priming that needs experimental confirmation based on studies with plant-soil systems: rhizosphere priming induced by the active plant release of specific compounds accelerating SOM mineralisation in response to stress conditions.