Necromass mass loss and microbial abundance for necromass interactions study

Soil organic matter (SOM) is increasingly recognized as a key component of
terrestrial carbon cycling, yet the relative contribution of microbial
necromass—and especially fungal necromass—remains poorly understood. We
produced fungal necromass of different biochemical quality (low vs. high
melanin content) from Hyaloscypha bicolor and decomposed it in forest
topsoil to study (i) how microbial decomposer and predator communities
differ between soil and necromass, (ii) whether necromass-associated
communities are subsets of bulk soil communities or contain additional
“unseen” colonizers, and (iii) if microbial predators (protists,
nematodes) exert top-down control on the necromass decomposers and
necromass decomposition rates. Over two sampling times (4 and 12 weeks),
necromass consistently exhibited rapid early mass loss, followed by
reduced decay, and more strongly stabilized mass in high melanin residues.
Quantitative PCR revealed substantially higher bacterial and fungal
abundances in necromass relative to soil, especially for low melanin
necromass. Metabarcoding showed distinct decomposer communities in
necromass as compared to soil, with half or more of the observed necromass
taxa absent in bulk soils at the site level. Necromass also supported
differentiated predator communities, including a high nematode richness at
early decay stages and a predominance of protist bacterivores. Structural
equation modeling indicated that predator community composition influenced
both bacterial and fungal abundance, and marginally significantly affected
necromass decomposition rates. We conclude that fungal necromass acts as a
microbial “hotspot” enriched in specialized decomposers and predators, and
that predator–decomposer interactions can potentially regulate necromass
decay. Our findings highlight the need to integrate top-down control and
colonization processes into models of fungal necromass turnover and its
ultimate contribution to soil organic carbon.