Fire-induced rapid suppression of microbial necromass accumulation in a subtropical Cunninghamia lanceolata forest

Microbial necromass carbon (MNC) is crucial for soil organic carbon (SOC) stabilization. However, how wild fire influence MNC accumulation remains to be elucidated. Here, we investigate the MNC dynamic and related soil and microbial traits on the 10th, 30th, and 90th days following a wildfire in a subtropical forest. Wildfire significantly decreased total MNC, primarily driven by reductions in fungal necromass (FNC), while bacterial necromass remained unaffected. The immediate impact (day 10) featured a sharp FNC decline, largely attributed to direct combustion, pyrolysis, and volatilization of existing necromass by high temperatures. While microbial biomass carbon (MBC) was not significantly reduced on day 10, an overall decrease was observed during the study period. This sustained FNC reduction and the overall lower MBC levels (indicating reduced MNC formation) were linked to intensified post-fire carbon limitation (due to reduced fine root input), suppression of specific fungal groups, and increased microbial investment in extracellular enzyme activities over growth. Concurrently, increased N-acetylglucosaminidase activity, likely stimulated by a shift from phosphorus to carbon limitation and altered microbial network complexity, indicated accelerated FNC decomposition. Despite substantial MNC losses, its proportional contribution to SOC remained unchanged within 3 months, suggesting concurrent losses of other SOC components. These findings evaluated the direct fire-induced necromass destruction offering crucial insights into short-term MNC fate and SOC dynamics in fire-disturbed subtropical forests.