Soil management does not affect fungal necromass carbon accumulation, but rather its persistence by shaping soil microbial traits

Fungal necromass carbon (FNC) is recognized as a key component of soil organic carbon (SOC). Yet, the mechanisms underlying FNC accumulation and, mainly, its persistence are still poorly understood. Here, using ¹³C-necromass substrate from Trichoderma longibrachiatum, we tracked the FNC accumulation and its persistence (decay) rates into SOC functional pools (e.g., mineral-associated organic carbon and particulate organic carbon; MAOC and POC) in soils with similar texture, but under different long-term agricultural management (monoculture vs. agroforestry). In doing so, we tested the hypothesis that contrasting soil management practices affect FNC cycling by altering soil chemical, physical, and biological conditions. Collectively, our results show that soil management does not affect the FNC short-term accumulation, but rather its persistence. This persistence was higher in monoculture soils (and not agroforestry) and was strongly associated with variation in community-weighted traits, including physiological (e.g., growth rate), biochemical (e.g., enzymatic repertoire), and genomic traits (e.g., genome size and motility), which together explained FNC retention in MAOC (R² = 0.74) and POC (R² = 0.84). Our findings indicate that abiotic soil properties primarily control FNC accumulation, while microbial traits (mainly the enzymatic repertoire) regulate its subsequent cycling, providing key insights for parameterizing next-generation process-based SOC models.