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

Aim

Nitrogen (N) deposition and climate warming are the two most important factors driving soil N₂O 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 N₂O emissions remain unclear.

Location

Global.

Time Period

1986–2022.

Major Taxa Studied

Soil N₂O 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 N₂O 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 N₂O 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 N₂O 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 N₂O emissions and N functional gene abundances despite the positive correlation between N functional gene abundances and potential nitrification and denitrification rates, but soil N₂O 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 N₂O emissions.

Main Conclusions

Our findings indicate that N addition and warming substantially affect soil N₂O emissions and highlight the urgent need to incorporate key abiotic factors and temperature-driven microbial kinetics of soil N₂O emissions into theoretical and modelling research for predicting global N₂O emissions.