Necromass Interactions 16S Metagenome

Mycelial residues, also known as fungal necromass, represent a substantial fraction of soil organic matter (SOM) pools. Although microbial decomposers are increasingly recognized as key drivers in forming fungal necromass carbon stocks, the role of microbial predators in mediating the microbial decomposition of mycelial residues has not been explored. To address this gap, we produced fungal necromass of varying biochemical quality from Hyaloscypha bicolor and decomposed it in forest topsoil to investigate how microbial decomposer (bacteria and fungi) and predator communities (protists and nematodes) differ between soil and necromass. Additionally, we examined whether microbial predators influence the abundance of fungal necromass decomposers and indirectly affect fungal necromass decomposition rates. Over two sampling times (4 and 12 weeks), necromass consistently exhibited rapid early mass loss followed by reduced decay, with a more strongly stabilized mass in high melanin necromass. Quantitative PCR revealed substantially higher bacterial and fungal abundances in necromass relative to soil, especially for low melanin necromass. Metabarcoding showed distinct microbial decomposer communities in necromass as compared to bulk soil both for protist and nematode communities. Structural equation modeling indicated that predator community composition influenced both bacterial and fungal abundances early and late in decay, and marginally significantly affected necromass decomposition rates. We conclude that fungal necromass acts as a microbial 'hotspot' not just for microbial decomposers but also their microbial predators. Our results also highlight the need to explore further potential top-down controls by microbial predators of fungal necromass decomposer communities to better understand the formation of fungal-derived SOM.