Repeated labile carbon inputs trigger soil microbial necromass decomposition through increasing microbial diversity and hierarchical interactions

Microbial necromass substantially contributes to soil organic carbon (SOC) sequestration. However, the response of soil microbial necromass to fresh labile carbon (C) inputs and the underlying microbial mechanisms are poorly understood. In this study, we investigated the dynamics of soil microbial necromass following single and repeated labile C inputs in two typical agricultural soils, black soil (Mollisol) and red soil (Ultisol). Our results showed that labile C inputs triggered the decomposition of soil native microbial necromass, regardless of soil type and C input frequency. Following repeated glucose pulses, the microbial necromass decreased by 75 % and 41 % in black and red soils, respectively, in a week. While a single glucose pulse triggered a comparable decline in soil microbial necromass, which occurred gradually over an incubation period of 3-4 weeks. In contrast, the priming effect following a single glucose pulse was 2-3 fold higher than repeated pulses. Repeated glucose pulses increased microbial alpha-diversity and temporal succession of various K-strategists, enhanced the network complexity and the potential hierarchical interactions between bacteria, fungi and protists, but yielded 1.66 fold less microbial biomass compared to a single pulse. These changes explained variations in soil microbial necromass after glucose pulses. Furthermore, repeated glucose pulses enhanced the linkages between microbial attributes and the degradation of soil microbial necromass. MicroResp assay revealed that the capacity of microbial communities to degrade microbially derived residues was 1.29 and 3.60 fold higher in black and red soils with repeated glucose pulses, respectively, compared to a single pulse. Our findings provide comprehensive insights into the microbially-mediated processes that influence soil microbial necromass degradation following labile C inputs, with important implications for understanding the dynamics and stabilisation of soil microbial necromass.