Global effects on soil respiration and its temperature sensitivity depend on nitrogen addition rate

Soil respiration (Rs) plays a crucial role in regulating carbon (C) cycling in terrestrial ecosystems and the atmospheric carbon dioxide (CO2) concentration. However, the impact of nitrogen (N) addition on Rs and its temperature sensitivity (Q10) is poorly understood. Here, we used 1413 paired observations from 261 studies to explore how N addition affects Rs and its Q10 across terrestrial ecosystems on a global scale. Nitrogen addition increased autotrophic respiration in croplands, deserts and shrublands, but decreased it in grasslands, forests (including coniferous and deciduous forests) and wetlands. In contrast, N addition increased heterotrophic respiration in grasslands, wetlands and deserts, but decreased its Q10 across different ecosystem types other than deserts. Nitrogen addition decreased (p < 0.05) the overall Rs and its Q10 by 19.5 and 32.1%, respectively. The decrease in Rs in response to N addition might be attributed to a reduction in heterotrophic respiration. Moreover, the Rs and its Q10 decreased while soil organic C content increased with the increasing rate of N addition up to 100–150 kg ha−1 yr−1. The results suggest that 100–150 kg N ha−1 yr−1 was the optimum N addition rate to maintain the soil as a C sink. In addition, soil pH, C:N ratio and respiratory quotient were significant predictors of soil respiration and its Q10. Our study highlights that the N addition rate-dependent effects on Rs and its Q10, and soil organic C should be incorporated into global C models to improve the assessment of N addition effects on the global C cycle.