Simulated nitrogen deposition influences soil greenhouse gas fluxes in a Mediterranean dryland

Soil nitrogen (N) availability is a key driver of soil-atmosphere greenhouse gas (GHG) exchange, yet we are far from understanding how increases in N deposition due to human activities will influence the net soil-atmosphere fluxes of the three most important GHGs: nitrous oxide (NO), methane (CH) and carbon dioxide (CO). We simulated four levels of N deposition (10, 20 and 50 kg N ha yr, plus unfertilised control) to evaluate their effects on NO, CH and CO soil fluxes in a semiarid shrubland in central Spain. After 8 years of experimental fertilisation, increasing N availability led to a consistent increase in NO emissions, likely due to simultaneous increases in soil microbial nitrification and/or denitrification processes. However, only intermediate levels of N fertilisation reduced CH uptake, while increasing N fertilisation had no effects on CO fluxes, suggesting complex interactions between N deposition loads and GHG fluxes. Our study provides novel insight into the responses of GHGs to N deposition in drylands, forecasting increases in NO emissions, and decreases in CH uptake rates, with likely consequences to the on-going climate change.