Warming-Driven Biological Mechanisms Governing the Fate of Pyrogenic Organic Matter in Soil

Pyrogenic organic matter (PyOM) significantly contributes to soil carbon (C) sequestration, yet its stability in terrestrial ecosystems is more dynamic and biologically responsive than previously assumed. A thorough understanding of mechanisms governing PyOM stability is critical, given increased wildfire occurrence and associated PyOM production in a warming climate and the potential feedbacks to the global C cycle. This review highlights how warming-driven changes in soil biological processes directly and indirectly influence PyOM persistence. Our synthesis reveals that long-term soil warming initiates a cascade of competing biological processes. For example, warming enhances microbial oxidative enzyme activity and stimulates co-metabolic breakdown of labile PyOM components, notably its dissolved fraction, via greater plant-derived labile C input. Conversely, soil warming promotes mechanisms of stabilization, as microbial surface oxidation strengthens organo-mineral bonds and increased bioturbation by soil fauna transports PyOM fragments into deeper, mineral-protected soil layers. These opposing processes operate simultaneously, resulting in a dynamic balance between decomposition and stabilization. This balance may be further modified by warming-associated changes in soil moisture, which can suppress both decomposition and stabilization processes. Critically, the prevailing outcome is dictated by the intrinsic heterogeneity of the PyOM in question.  Low-temperature PyOM is more vulnerable to enhanced decomposition, while high-temperature, lignin-rich PyOM is more resistant to decomposition and enters stabilization pathways. We conclude that the net persistence of PyOM in a warming climate depends on the dynamic balance between biological decomposition and physicochemical stabilization, controlled by interactions among PyOM properties, soil biota, and environmental drivers.