A paradigm shift for rhizosphere priming effects to unearth new potential for more sustainable plant production?

Rhizosphere priming effects (RPE) are often assumed to accelerate soil organic matter turnover and drive net carbon loss from soils, thereby amplifying climate warming via CO2-feedbacks. Here, this paradigm is challenged combining empirical evidence and a stoichiometric model to show that co-occurring positive and negative RPE can cancel each other over time, resulting in neutral or positive net effects on the soil carbon balance. Then, several data streams are united to caution against upscaling reductionist laboratory soil incubations to ecosystem processes, because they consistently overestimate RPE, related to sieving disrupting the physical integrity of soil minerals and because food webs in natural ecosystems buffer the effects of labile C-inputs so that priming in nature has less extreme magnitudes than in soil incubations. Monte-Carlo simulations further demonstrate that even modest isotopic and flux measurement errors can generate spurious priming estimates when isotopic contrast is weak, highlighting the need for improved methodical accuracy to draw robust conclusion about priming in vivo. In conclusion, it is suggested RPE might function as a mechanism to synchronize carbon and nutrient supply and demand in the rhizosphere, rather than a consistent driver of soil carbon loss, with more modest effects in the field than in the lab. Future research prioritizing experiments with living plants at high labelling intensities, linking C and N fluxes and holistically accounting for the net carbon balance with respect to plant, soil and biota pools and fluxes will provide a more accurate foundation for the conceptualization of rhizosphere contributions to ecosystem carbon and nutrient cycling.