Patterns and drivers of soil autotrophic nitrification and associated N2O emissions

Soil autotrophic nitrification, driven by ammonia oxidizers, is critical for providing plant-available nitrogen (N). However, it can also lead to N losses and environmental degradation under certain conditions. While numerous studies have examined autotrophic nitrification at individual sites, there is a lack of broad-scale, systematic investigations across diverse biomes, soil types, and climatic conditions. To address this gap, we analyzed data from 52 studies that used shaken slurry or aerobic incubation experiments that used chemical inhibitors (1octyne and acetylene) to distinguish autotrophic nitrification driven by different taxa of ammonia oxidizers. Our analysis showed significant variation in nitrification rates, N2O emissions, and N2O yield across different ecosystems and fertilizer types. Croplands and soils treated with organic fertilizers exhibited the highest risk of N losses, whereas partially substituting mineral fertilizers with organic fertilizers showed the potential in reducing this risk. The observed inconsistent variations in autotrophic nitrification rates and N2O emissions are likely due to changes in N2O yield. Optimal temperatures for autotrophic nitrification were higher for ammonia-oxidizing archaea than for ammonia-oxidizing bacteria and varied across ecosystems and fertilizer types, reflecting the unique environmental conditions shaping ammonia oxidizer communities. The abundance of ammonia oxidizers was the primary factor regulating total autotrophic nitrification rates. Based on these findings, we suggest two strategies to control autotrophic nitrification: reducing substrate availability by incorporating organic or mixed fertilizers and applying nitrification inhibitors. In conclusion, this study provides a comprehensive overview of soil autotrophic nitrification across a broad range of conditions, contributing to a deeper understanding of soil N dynamics and informing nutrient management strategies to reduce N losses and environmental pollution.