Root and mycorrhizal contributions to soil organic carbon changes following 12 years of poplar coppice on former cropland and grassland.

Background and Aims: The establishment of bioenergy plantations as short-rotation coppice poplar systems has been proposed as a sustainable strategy to mitigate climate change through carbon capture. This study evaluates changes in soil organic carbon (SOC) after 12 years of poplar cultivation on former cropland and grassland in Belgium using repeated soil sampling to assess SOC stock changes and in-growth cores to identify carbon input pathways. Methods: Using isotope tracing and in-growth cores with treatments excluding roots, mycorrhizae and above-ground inputs, we quantified the contributions of roots, mycorrhizae, and dissolved organic matter to new SOC formation and their interaction with the mineralization of native SOC. Results: Results showed a significant increase in SOC in former croplands while grasslands experienced a slight SOC reduction, highlighting the influence of previous land use on SOC accrual potential. Root-derived inputs surpassed mycorrhizal contributions to SOC formation although both played a role in achieving a positive SOC balance. Conclusion: This study underscores the critical role of roots in SOC accumulation and the importance of initial soil conditions when designing SOC accrual strategies through bioenergy plantations. Supplementary Information: The online version contains supplementary material available at 10.1007/s11104-025-07995-2.