Intrinsic and extrinsic controls on the decomposition of fungal necromass

Soil organic matter represents the largest active reservoir of organic carbon in terrestrial ecosystems, playing a critical role in atmospheric carbon capture and climate change mitigation. Recent studies have demonstrated that mycelial residues, also known as fungal necromass, contribute significantly to fungal necromass stocks in soils. While the magnitude and distribution of fungal necromass stocks are increasingly well documented, the processes driving their formation remain poorly understood. Specifically, the transformation of recently senesced mycelial residues into stabilized soil organic matter during the early stages of decomposition is not fully elucidated. These residues form an ephemeral resource patch of energy and nutrients for soil microbial decomposers, with the unique aspect that the microorganisms responsible for producing them also serve as their primary decomposers, contrasting with the decay of plant residues. Thus, new concepts, theories, and approaches are needed to understand fungal necromass decomposition. Here, we assess the intrinsic drivers of necromass decay by evaluating how the physiological status of fungi at the time of death influences decomposition processes, and explore extrinsic drivers by characterizing the biodiversity and functional traits of microbial decomposer communities—including fungi and protists. Our goal is to develop a refined conceptual and research framework for microbial residue decomposition and promote the integration of these processes into soil biogeochemical models.