Impact of global warming on Soil Organic Matter pools and crop yields

Climate change is expected to profoundly alter both soil functioning and crop productivity, yet important uncertainties remain regarding the short-term response of soil organic carbon (SOC) to warming in temperate agroecosystems. This thesis investigates how climate manipulation (warming; +2 °C) influences SOC dynamics, soil processes, and crop performance within a soybean–sugar beet rotation system in northern Italy. A two-year field experiment (2023–2024) was conducted using open-top chambers (OTCs) under a randomized complete block design. This experimental approach was combined with advanced soil fractionation techniques, elemental and thermal analyses, and process based crop modelling to provide a multi-scale understanding of warming effects, from soil local processes to continental-scale projections. Results revealed that warming consistently increased soil temperature while reducing soil moisture, leading to enhanced soil respiration across all systems. However, despite this stimulation of carbon fluxes, bulk SOC stocks remained remarkably stable over the short term, highlighting a decoupling between rapid carbon turnover and more persistent soil carbon pools. In contrast, crop identity and interannual variability emerged as dominant drivers of SOC dynamics and soil physical and chemical properties, with soybean systems generally promoting higher SOC stocks and more favourable C/N ratios than sugar beet. The partition of SOC into mineral associated organic matter (MAOM) and particulate organic matter (POM) showed that SOC is largely dominated by MAOM (78–84%), confirming the central role of mineral-associated pools in carbon stabilization. While warming did not significantly alter total SOC stocks, it induced subtle but meaningful shifts in SOC allocation and stoichiometry that were strongly crop-dependent. In particular, warming increased the contribution of labile carbon in sugar beet systems and enhanced microbial processing in soybean soils, as reflected by changes in the MAOC/POC ratio and C/N dynamics. Thermogravimetric analyses further revealed distinct signatures between SOM fractions, emphasizing fundamental differences in their stabilization mechanisms. Notably, thermal stability indices remained largely insensitive to warming, suggesting that short-term temperature increases primarily affect SOC distribution and quality rather than its intrinsic stability. Correlation analyses supported this interpretation, showing that warming modifies the relationships among stoichiometric, thermal, and energetic properties of SOC in a crop-specific manner. At the crop level, warming strongly reduced sugar beet and soybean yields (~70-80%), whereas sugar beet quality remained relatively stable. By integrating field observations with AquaCrop-based simulations and large-scale (European) geospatial datasets, this thesis provided insights into future climate scenarios and highlighted the importance of SOC management for sustaining crop productivity. Overall, this work demonstrates that short-term warming in temperate agroecosystems does not necessarily lead to immediate SOC losses, but rather reshapes SOC relative distribution. Finally, it identifies crop type and rotation as key modulators of soil responses to warming, underscoring the need to integrate soil carbon processes, crop management, and climate projections to improve predictions of agroecosystem resilience under ongoing climate change.