Soil microbial respiration does not respond to nitrogen deposition but increases with latitude

Facing global changes, substantial modifications in soil microbes and their functions have been widely evidenced and connected. However, the response of soil microbial respiration (MR) to increasing nitrogen (N) deposition and the role of microbial characteristics in controlling this response remain elusive. In this study, we quantified the intensity of the soil MR in terrestrial ecosystems that suffered elevated N deposition. High-throughput quantitative sequencing and phospholipid fatty acids were employed to analyse microbial community properties and biomass, whilst microbial necromass was quantified using biomarker amino sugars. Our results revealed that soil MR kept stable under N deposition. Microorganisms maintained their respiration rates by modifying the characteristics of enzymes rather than altering microbial community properties or biomass. Notably, soil MR increased with latitude across study sites, which was attributed to the restriction of microbial activity by bacterial necromass. Supporting this observation, the recalcitrance of the soil carbon (C) pool to microbial degradation was evidenced to be the stability mechanism underlying the spatial variations in MR. Overall, we propose that MR is resistant to short-term N deposition, whilst it exhibits a pronounced latitude dependence as shaped by the recalcitrant C pool. Our findings provide crucial insights into the microbial mechanisms of soil C dynamics under global change, contributing to the advancement of soil C models.