Microbial necromass plays a crucial role in soil organic carbon (SOC) formation, yet the underlying abiotic and biotic factors remain poorly understood, particularly the trophic interactions between protists and fungi/bacteria that drive soil fungal and bacterial necromass accumulation. A groundbreaking 27-year field study reveals that how soil protists differentially control fungal and bacterial necromass accumulation—a key process governing SOC storage. These findings, published in Soil Ecology Letters, redefine our understanding of soil carbon dynamics.

Professor Ding said, “Trophic interactions regulate soil microbial communities and play an important role in influencing microbial necromass dynamics. Protists, a major component of the soil micro-food web, have been shown to affect CO₂ release by microbes. This is achieved by directly decomposing fungal and bacterial byproducts and residues, and indirectly controlling bacterial and fungal community structure and function by consuming living microbial biomass. Although several studies have investigated the effects of protist-induced trophic interactions on soil microbiota, their feedback on microbial necromass accumulation remains unclear.”

In this study, based on a 27-year field fertilization experiment in upland Ultisols, they investigated how changes in fungal and bacterial necromass relate to the abundance, diversity, community structure, and trophic co-occurrence networks of microbial communities, including fungi, bacteria, and protists. The results showed that fungal necromass contributes 32.4% to SOC on average—more than double the contribution of bacterial necromass (14.6%). This was attributed to Ascomycota’s higher carbon efficiency and the recalcitrance of fungal cell walls. Interestingly, protists played a dual role in regulating microbial necromass: while protists suppressed ​​fungal necromass​​ accumulation by directly decomposing fungal residues, they enhanced ​​bacterial necromass​​ by boosting bacterial abundance. Additionally, soil total nitrogen had a substantial impact on the persistence of bacterial necromass, as bacterial residues are generally regarded as readily accessible resources. This study underscores protists’ underappreciated role in SOC formation, and has significant implications for improving forecasts of long-term carbon sequestration potential in agricultural systems and contributes to a deeper understanding of terrestrial carbon cycling processes in the context of novel climate conditions.
DOI​​：10.1007/s42832-025-0336-9