Microbial necromass carbon (MNC) is a major component of soil organic carbon and is impacted by the interactions between substrate quality and microbial communities. However, the microbial mechanism by which dissolved organic matter (DOM), as an active substrate, regulates MNC accumulation remain unexplored. This study identified the key driving pathways of MNC accumulation in topsoil (0–20 cm layer) and subsoil (20–40 cm layer) using a long-term field experiment initiated in 1990, including chemical fertilizer (CF), CF combined with straw (SCF) or manure (MCF), and an unfertilized control (CK). Results showed that, compared to CK, the SCF and MCF treatments significantly increased MNC content by 31.6% and 38.2% in the topsoil, and by 20.0% and 35.6% in the subsoil, respectively. The application of organic materials (SCF and MCF) transformed labile into refractory DOM through thermodynamically limited process, leading to a shift in DOM degradation from rapid bacterial consumption to slower fungal processing. Further analysis revealed that the SCF treatment promoted fungal network modularity and necromass accumulation by altering the molecular weight of DOM. Whereas MCF treatment enhanced bacterial necromass accumulation by enriching specialized bacterial taxa through DOM with higher aromaticity. Interestingly, the predictors of MNC accumulation shifted from a multi-factor synergy in the topsoil to a DOM-dominated (explaining 66.6% of the variation) pathway in the subsoil. Overall, our findings highlight the central role of DOM in microbially mediated MNC accumulation and provide mechanistic insights linking DOM characteristics to agricultural management strategies. • Organic materials shifted DOM degradation from bacterial to fungal pathways. • Straw promoted fungal necromass through DOM molecular weight and fungal modularity. • Manure promoted bacterial necromass through DOM aromaticity and bacterial community. • DOM more strongly drives MNC in the 20-40 cm than in the 0-20 cm layer.
Zhu et al. (Sun,) studied this question.