Microbial metabolic quotient of soil nitrogen mineralization: Global patterns and controlling factors

Soil nitrogen mineralization is crucial for the sustainability of available soil nitrogen and hence ecosystem functioning. Microbial metabolic quotient of nitrogen mineralization (Q_min) determines the efficiency of soil nitrogen turnover. However, it is far from clear how Q_minchanges with the environment at the global scale. We compiled 871 observations of soil Q_minfrom 81 published articles across terrestrial ecosystems (croplands, forests, grasslands, and wetlands) to elucidate the global patterns of soil Q_minand its controlling factors. Soil Q_mindecreased from the equator to two poles and correlated negatively with soil pH, total soil nitrogen, the ratio of soil carbon to nitrogen, and soil microbial biomass carbon, but positively with mean annual temperature and carbon: nitrogen ratio of soil microbial biomass at a global scale. The results of structural equation models (SEM) showed that carbon: nitrogen ratio of soil microbial biomass was the foremost factor correlated with soil Q_min. Moreover , the significantly positive relationships between soil Q_minand carbon: nitrogen ratio of soil microbial biomass were consistent across ecosystem types. Soil microbial biomass, climate, and soil physical and chemical properties in combination accounted for 41% of the total variation of global soil Q_min. Our findings suggest that soil nitrogen cycling will accelerate under global warming and higher carbon: nitrogen ratio of soil microbial biomass viastimulating soil Q_min, and indicate the possibility for incorporating soil Q_mininto Earth system models to better predict nitrogen cycling under environmental change.