Role of aromatic and non-protonated aromatic carbon in the stability of soil organic matter

Research on soil organic matter (SOM) in its natural state is vital for comprehending the mechanisms governing soil stability and carbon cycling, crucial in addressing global climate change. We utilized solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy on HF treated samples, along with a 260-day laboratory mineralization experiment and thermal analysis-programmed pyrolysis (PP) to evaluate SOM biodegradability and thermal stability. To cover the potential range of organic carbon variability, we selected samples from three land uses and soil types, featuring total organic carbon levels from 1% to 39%. Our analysis confirmed the substantial contribution of non-protonated aromatic-carbon not bonded to oxygen to SOM’s biological and thermal stability, constituting approximately 14–21% of soil organic carbon. These components exhibited a strong correlation with SOM stability matrices, such as thermal stability and oxygen index determined by PP. Samples with a higher prevalence of these components also displayed the lowest cumulative carbon mineralization. These findings enhance our understanding of the stable SOM pool, aiding in the identification of sustainable soil management practices to mitigate climate change impacts on soil health and carbon dynamics.