Microbial recalcitrant-C metabolism and community composition shifts support enhanced thermal adaptation of soil microbial respiration

Understanding microbial thermal responses along natural climate gradients is crucial for improving predictions of carbon-climate feedbacks. However, the mechanisms by which variations in microbial carbon metabolic strategies and community composition modulate thermal responses of microbial respiration remain poorly understood. Here, we investigated thermal responses of microbial respiration along an elevational temperature gradient with and without glucose addition, focusing on the roles of microbial carbon metabolic strategies and community composition in shaping microbial thermal responses. Our results revealed that microbial respiration exhibited enhanced adaptation to increasing mean annual temperature (MAT) of the sampling sites, and glucose addition further promoted the magnitude of enhanced thermal adaptation in both surface and subsurface soils. This pattern suggests a positive feedback of microbial carbon decomposition to warming. Metabolism of recalcitrant carbon compounds and enzymatic activities related to recalcitrant carbon oxidation increased with MAT, explaining the largest variation in the enhancement magnitude of microbial respiration. These specific microbial carbon metabolic strategies were linked to microbial carbon availability and shifts in microbial community structure toward oligotrophic microbial strategies. Overall, enhanced thermal adaptation of microbial respiration was associated with increased decomposition of recalcitrant carbon, driven by elevated enzymatic oxidation activity and a microbial community shift toward higher oligotrophic strategists, potentially alleviating microbial substrate limitations. Our findings highlight a mechanism whereby altered microbial carbon metabolic strategies may amplify soil carbon loss by mitigating substrate limitations under warming conditions.