Do poplar plantations enhance organic carbon stocks in arable soils? A comprehensive study from Northern Italy.

Soil organic carbon (SOC) depletion, primarily driven by land use change, is a global challenge influenced by factors such as climate, plant cultivation, and adopted management practices. Poplar plantations (PP), predominantly used for plywood and bioenergy production in the Mediterranean, have shown carbon (C) potential capture as biomass. However, their contribution to SOC and climate change mitigation remains understudied. Thus, this study evaluates the potential of PP in enhancing SOC stocks in arable soils in Northern Italy covering fifteen sites within six farms. SOC stocks under land use change were analyzed, at 0-10 and 10-30 cm soil depths, using the time-for-space substitution method (paired comparison), comparing cropland (CR) to PP, and spatial survey approach evaluating SOC after thirty years of PP. Additionally, conventional PP was also compared with c plantations (PC), which integrate diverse tree species supporting biodiversity and fostering sustainability. Results showed that PP maintains higher SOC stock than CR management, with significant variations observed in fifty percent of the cases. Relative SOC sequestration rates were 0.09 and 0.32 Mg C ha year at 0‒10 and 10‒30 depth, respectively. The mean SOC rate for PP was 0.75 Mg C ha year under stock differential methods, with the initial C loss observed in the early stages (1‒5 years). PC demonstrated greater SOC stocks and sequestration rates, indicating its potential for climate change mitigation through European policies. Overall, this study shows PP has potential for C sequestration varies by sites. Further investigation into fertilization and deep-soil tillage is needed to understand their impact on SOC stocks. Moreover, direct engagement with PP farmers revealed supply chain issues, highlighting the need for sustainability improvement.