<b>Intensified spatial divergence of fungal and bacterial necromass carbon under climate change masks global soil carbon vulnerability</b>

Here, we synthesised 2,958 observations from 352 studies, using machine learning alongside driver analysis to reveal geographically distinct hotspots of relative enrichment for fungal necromass carbon (FNC) and bacterial necromass carbon (BNC). FNC showed a spatial pattern similar to that of total MNC and was relatively enriched in high-latitude and montane regions, whereas BNC contributed proportionally more in humid tropical regions.

This divergence may arise from the long-term interplay among necromass formation, decomposition, and persistence processes, whereby FNC retention is predominantly governed by hypha-mediated aggregation, whereas BNC accumulation is preferentially shaped by moisture-driven turnover and mineral association. Under the SSP245 scenario, the non-significant change in total MNC masked divergent FNC and BNC responses. FNC declined mainly in humid tropical (15.5%) and subtropical/warm temperate (10.9%) regions, which together accounted for 12.4% of FNC loss, whereas BNC increased by 11.3% in humid tropical regions.

This internal compositional shift may alter regional climate sensitivity and increase carbon vulnerability, which warrants close attention.d persistence processes, whereby FNC retention is predominantly governed by hypha-mediated aggregation, whereas BNC accumulation is preferentially shaped by moisture-driven turnover and mineral association. Under the SSP245 scenario, the non-significant change in total MNC masked divergent FNC and BNC responses.

FNC declined mainly in humid tropical (15.5%) and subtropical/warm temperate (10.9%) regions, which together accounted for 12.4% of FNC loss, whereas BNC increased by 11.3% in humid tropical regions. This internal compositional shift may alter regional climate sensitivity and increase carbon vulnerability, which warrants close attention.</p>