Microbial life-history strategies mediate temperature effects on organic carbon pools in black soils

POC content increased and MAOC content decreased with increasing mean annual temperature. Bacterial life-history strategies shifted from K- to r-strategists with warming. r-strategists prevalence induced stronger bacterial-saprotrophic fungi associations. r-strategists and saprotrophic fungi caused higher POC and lower MAOC content. Partitioning of soil organic matter for particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) is essential to understand carbon (C) storage under climate change, given their distinct properties and response to warming. The mechanisms underlying warming-induced changes in C pools in black soils (Mollisols) remain unknown, owing to the stability of C pools and the complexity of their associated microbial communities. This study elucidates POC and MAOC contents and their microbial controls in black soils along a mean annual temperature (MAT) gradient from 0.6 to 7.3 °C. The POC content (3.3–17 g kg−1) increased with MAT, while MAOC content (33–60 g kg−1) decreased, indicating accelerated C turnover with warming. Higher MAT shifted the bacterial communities from K- to r-strategies, aligning with increased POC content. The dominance of r-strategists facilitated rapid utilization and mineralization of organic compounds (e.g., mainly with low C/N ratio), reducing MAOC and increasing POC through sustained plant residue inputs. This shift towards r-strategists also corresponded with increased abundance of saprotrophic fungi and stronger bacteria–saprotrophic fungi associations. Warming in colder regions may release available organic matter that saprotrophic fungi preferentially utilize over plant residues to minimize energy expenditure, decreasing POC decomposition. Our findings suggest that integrating microbial r-/K-strategies help to elucidate these mechanisms and simplify the interpretation of temperature effects on the dynamics of two main functional pools of soil organic matter. © 2025 Elsevier B.V., All rights reserved.