Global variations and controlling factors of soil nitrogen turnover rate

Soil nitrogen (N) availability, which is crucial to plant growth, largely relies on the turnover of soil organic N into inorganic N through mineralization. However, the patterns and drivers of global soil N turnover rates (NTR) have not been carefully examined so far. We compiled a dataset that consists of 1175 observations from 159 published articles across various terrestrial ecosystems in the world. Our analysis of this dataset showed that changes in soil NTR successfully predicted global NH4+–N content, a key indicator of soil N availability. Our analysis also revealed a clear latitudinal pattern of soil NTR, which was high in low latitude but low in high latitude. Soil NTR was greater in croplands than grasslands and wetlands. The dominant driving variables were mean annual temperature which accounted for 23% of the total variation in soil NTR. Soil clay content explained 15% of the total variation and it strongly inhibited soil NTR. However, the key driver in soil NTR differed with ecosystem type, i.e. soil microbial biomass in croplands, clay content in forests and grasslands, and soil C:N ratio in wetlands. This study highlights the importance of climatic factors and soil properties on soil NTR, which should be integrated into biogeochemical models to better predict the changes of soil N availability at the global scale.