Exploring Global Data Sets to Detect Changes in Soil Microbial Carbon and Nitrogen Over Three Decades

Understanding the temporal dynamics of soil microbial biomass is crucial for assessing soil ecosystem functions and services, yet these dynamics are globally uncertain. Here, we compiled a data set of soil microbial biomass carbon (MBC) and nitrogen (MBN) from 1493 studies between 1988 and 2019 to elucidate their temporal trends and potential drivers. Results showed that global MBC and MBN significantly decreased by 0.033 Mg C ha⁻¹ yr⁻¹ and 0.007 Mg N ha⁻¹ yr⁻¹ at 0–30 cm soil depth, between 1988 and 2019, respectively, which might be primarily attributed to the warming of the climate, the increase in global precipitation, and reduction of soil organic carbon (SOC) stock. The rate of decline in MBC and MBN showed a non-linear trend: following a decline from 1988 to 1999, it slowed down until 2014, likely due to the global warming hiatus. Afterward, the pace of decline increased again from 2015 to 2019. Boreal biomes experienced the largest decrease in soil microbial biomass with the reduction rate of MBC being 4.3 times higher than in temperate biomes, showing a higher sensitivity in boreal biomes to climate change. Grassland ecosystems also exhibited greater reductions, possibly driven by their degradation. These findings shed valuable insights on the long-term dynamics of soil microbial biomass on a global scale over the last three decades. Furthermore, this study underscores the importance of preserving soil microbial biomass as a key strategy to mitigate the adverse effects of future climate change, thereby sustaining ecosystem health and resilience.