Variations in Soil Available Nitrogen Rather Than Nitrogen Functional Gene Abundances Dominate Terrestrial Soil <scp>N₂O</scp> Emissions Under Mineral Nitrogen Addition and Warming

ABSTRACT Aim Nitrogen (N) deposition and climate warming are the two most important factors driving soil N 2 O emissions in terrestrial ecosystems. Both biotic and abiotic factors impact N cycling processes and functional gene abundances, but their global responses and patterns to mineral N addition and warming and the regulatory factors affecting N 2 O emissions remain unclear. Location Global. Time Period 1986–2022. Major Taxa Studied Soil N 2 O emission, N functional gene abundances and edaphic factors. Methods We synthesised 5299 observations of soil N cycling processes, functional gene abundances and edaphic factors under mineral N addition and warming from 357 peer‐reviewed publications worldwide. Results We showed that mineral N addition and warming increased soil N 2 O emissions by 199.9% and 32.4%, respectively. N functional gene abundances, potential nitrification and denitrification rates were less sensitive to warming, and the responses of N 2 O emissions and N functional gene abundances were independent of biome, N form and warming method. Changes in N cycling processes and functional gene abundances are related to climates, edaphic factors and experimental manipulations, and spatial heterogeneity in the response of N 2 O emissions and N functional gene abundances to N addition and warming has been observed across the world. There was no clear relationship between changes in soil N 2 O emissions and N functional gene abundances despite the positive correlation between N functional gene abundances and potential nitrification and denitrification rates, but soil N 2 O emissions increased with increasing soil available N under both N addition and warming. Our results suggest that abiotic factors are the key reason for N‐induced changes in N 2 O emissions. Main Conclusions Our findings indicate that N addition and warming substantially affect soil N 2 O emissions and highlight the urgent need to incorporate key abiotic factors and temperature‐driven microbial kinetics of soil N 2 O emissions into theoretical and modelling research for predicting global N 2 O emissions.