Substrate quality drives fungal necromass decay and decomposer community structure under contrasting vegetation types

1. Fungal mycelium is increasingly recognized as a central component of
soil biogeochemical cycling, yet our current understanding of the
ecological controls on fungal necromass decomposition is limited to single
sites and vegetation types. 2. By deploying common fungal necromass
substrates in a temperate oak savannah and hardwood forest in the
midwestern USA, we assessed the generality of the rate at which high- and
low-quality fungal necromass decomposes; further, we investigated how the
decomposer ‘necrobiome’ varies both across and within sites under
vegetation types dominated by either arbuscular (AM) or ectomycorrhizal
(EM) plants. 3. The effects of necromass quality on decay rate were robust
to site and vegetation type differences, with high-quality fungal
necromass decomposing, on average, 2.5 times faster during the initial
stages of decay. Across vegetation types, bacterial and fungal communities
present on decaying necromass differed from bulk soil microbial
communities and were influenced by necromass quality. Moulds, yeasts and
copiotrophic bacteria consistently dominated the necrobiome of
high-quality fungal substrates. 4. Synthesis: We show that regardless of
differences in decay environments, high-quality fungal substrates
decompose faster and support different types of decomposer microorganisms
when compared with low-quality fungal tissues. These findings help to
refine our theoretical understanding of the dominant factors affecting
fast cycling components of soil organic matter (SOM) and the microbial
communities associated with rapid decay.