Three decades of continuous warming in temperate forests destabilizes persistent forms of soil organic matter

Rising temperatures have altered the balance of soil carbon stored versus respired in forest ecosystems worldwide. Yet, the molecular-level mechanisms driving changes to soil biogeochemical processes and the long-term changes to soil organic matter (SOM) dynamics remain unclear. Thus, we leveraged the world's longest soil warming experiment, spanning over three decades in a temperate forest, to investigate changes in SOM chemistry and microbial responses. Using advanced molecular-level techniques, we identified significant perturbations to SOM composition and novel shifts in microbial degradation pathways. Chronic warming enhanced the breakdown of plant-derived lipids typically thought resistant to microbial decomposition. Concomitant shifts in microbial communities indicate altered carbon use strategies, with microbes acclimating to warming and increasingly targeting persistent compounds. We provide new molecular-level evidence that chronic warming disrupts chemically resistant carbon compounds through altered microbial breakdown, revealing mechanisms by which persistent SOM pools may be lost. This further demonstrates that long-term stability is not solely governed by intrinsic chemical properties. Our findings underscore the need to fully elucidate long-term microbial functional shifts and their impacts on the stability of persistent SOM pools in a changing world. • Sustained soil organic matter breakdown after 32 years of warming. • Persistent plant-derived n -alkanes declined under chronic soil warming. • Shifts in microbial carbon utilization strategies and efficiency. • Enhanced degradation of chemically stable organic matter. • Revealed a mechanism capable of destabilizing persistent soil carbon pools.