We investigated the decomposition of diverse root-associated fungi, their influence on native soil carbon dynamics and the relationship of these processes with fungal traits. We quantified the decomposition of 13C-labelled mycelium of fourteen species, their priming of native soil carbon, impact on functional soil carbon pools, microbial use of carbon and microbial community size and composition and evaluated chemical, morphological, and physiological traits of the fungi to investigate their potential to control carbon processes. Fungal C/N, melanin and growth rates were linked to necromass decomposability and its stabilisation. Necromass addition commonly caused suppression of native soil carbon decomposition (negative priming), including that of the resistant pool, and this suppression was stronger as fungal decomposability decreased. We provide novel, clear evidence of linkages between root-associated fungal traits, necromass decomposition, microbial C use and soil C stability which builds our mechanistic understanding of the role of dead fungi on soil C storage.