Estimating Rhizosphere Priming in European Agricultural Soils

The rhizosphere priming effect (RPE) is a key process where the mineralization of soil organic carbon (SOC) by microorganisms is modified by the presence and activity of plant roots compared to SOC mineralization on bare soil, increasing carbon fluxes from soils to the atmosphere. However, its magnitude in agricultural systems remains uncertain. Moreover, since the RPE is not specifically accounted for in earth system models it is a source of uncertainty in global carbon loss estimates relevant to achieve climate change targets. The PrimeSCale model offers a simple framework to quantify RPE-induced SOC respiration at large spatial scales. Here we aim to estimate the RPE in specific European croplands.

The PrimeSCale model estimates the RPE using root carbon input to the soil derived from the combination of MODIS gross primary production (GPP) and net primary production (NPP) data, root depth distribution, heterotrophic respiration, soil bulk density and soil organic carbon content. A central component of PrimeSCale is the RPE ratio, the relative increase in heterotrophic respiration induced by priming based on literature using living plants. Our analysis of the time period 2010-2020 covers six types of croplands (maize, wheat, oat, barley, legumes, and soy) across Europe at a 5 km resolution, down to a depth of 200 cm. The model outputs include the magnitude of the RPE ratio and RPE-induced SOC loss in these croplands and how they vary within Europe according to climate and crops. Our findings will enhance understanding of the processes behind carbon cycling in managed environments and provide insights for carbon-farming policies to better suit mitigation strategies.