Trade-offs between microbial growth yield and resource acquisition govern the long-term fertilized soil organic...

Agriculture is expected to play a significant role in supporting carbon (C) sequestration globally. Microbial carbon use efficiency (growth yield, Y-strategy) and enzyme production (resource acquisition, A-strategy) are fundamental life history traits that affect soil C balance. Yet, uncertainties persist concerning microbial adaptations to long-term fertilization and the ensuing regulation of C cycling. Here, we investigated the trade-offs between Y-strategy and A-strategy, as well as their impacts on C accumulation in red soils (C-poor) and yellow soils (C-rich) subjected to 30 years of chemical and organic fertilization. We found that long-term fertilization exerts context-dependent effects on microbial Y-strategy (growth yield) and A-strategy (resource acquisition): in red soils, microbial Y- and A-strategies exhibit a significant trade-off-microbial Y-strategy is enhanced whereas A-strategy is reduced, jointly regulating C accumulation. Conversely, in yellow soils, a synergistic trend emerges only under mineral (NPK) and organic (NPKM) fertilization, with Y-strategy alone driving C accumulation. Further analysis revealed that soil stoichiometry and microbial traits strongly account for strategy variations by driving C-stable genes across soils: in red soils, higher C:P and N:P ratios (reflecting nutrient availability) favor dominance of k-strategist Acidobacteria, strengthening microbial A-strategy by upregulating C-stable genes related to resource acquisition, which creates a marked trade-off with the Proteobacteria-dominated Y-strategy. In yellow soils, however, altered nutrient availability weakens such functional differentiation among microbial groups, dissipating the Y-A trade-off. Notably, specific fertilization (e.g., N, NPK, NPKM) drives a synergistic trend via sufficient nutrient supply. Overall, our findings suggest that trade-offs between microbial growth yield and resource acquisition govern soil organic carbon (SOC) after long-term fertilization, revising the previous assumption that a high CUE promotes microbial biomass, enzyme production, and organic matter decomposition.