Additive effects dominate phosphorus offsetting positive effects of nitrogen to terrestrial ecosystem N2O emissions

Nitrous oxide (N₂O) emissions from terrestrial ecosystem significantly contribute to global warming and are substantially influenced by nitrogen (N) and phosphorus (P) additions. Yet, the precise interactive effects of N and P addition on N₂O emissions remain poorly understood. We synthesized 714 observations from 198 publications to evaluate the response of N₂O emission rates to N and P addition across terrestrial ecosystems. Our results revealed that N and nitrogen + phosphorus (NP) additions increased N₂O emissions by 122.5 % and 64.5 %, respectively. In contrast, P addition alone reduced N₂O emissions by 16.3 %. Akaike mixed model weights identified ecosystem type as a factor commonly influencing N₂O emissions under added N, P, and NP. Predominantly additive interactions between N and P additions drove N₂O emission responses, rather than synergistic or antagonistic interactions. Antagonistic effects were exclusively observed in cropland ecosystems. Collectively, these findings demonstrate that N and P addition exhibit independent and additive effects on N₂O emissions in terrestrial ecosystems. This implies that the stimulatory effect of N and the inhibitory effect of P can be quantitatively combined to improve predictions of N₂O emissions under nutrient enrichment scenarios.