How do natural soil NH4+, NO3− and N2O interact in response to nitrogen input in different climatic zones? A global meta‐analysis

Abstract

AbstractThe increase of fossil‐fuel burning and nitrogen (N) fertilizer consumption continues to elevate global N deposition, leading to significant increases of soil NH4+ and NO3− concentrations, and thus N2O emissions. This is especially important for natural, unmanaged soils which are considered as areas that are sensitive to N input. However, uncertainties exist regarding the interactions of soil N2O emissions with soil NH4+ and NO3− concentrations in response to N input in different climatic regions, as well as their underlying potential mechanisms. Here, we conducted a meta‐analysis to investigate the responses of these three forms of N to external N input across global natural ecosystems, using data extracted from peer‐reviewed studies. The results show that soil NO3− concentrations are increased to a much larger extent by N input in temperate regions (136%) compared to tropical (62%) and subtropical (54%) regions, whereas the increase of soil NH4+ concentrations by N input is much less than soil NO3− concentrations, at 20%, 26% and 28% in temperate, tropical and subtropical regions, respectively. The significantly larger increase in soil NO3− concentrations but slightly lower increase in soil NH4+ concentrations in temperate regions compared to other climatic zones may be ascribed to the dominant nitrification process in temperate areas, which promotes the conversion of NH4+ to NO3−. Soil N2O emissions were increased to the greatest extent in subtropical regions (348%) in response to N input, followed by temperate regions (111%) and tropical regions (44%), which may be a result of the dominant denitrification process in subtropical regions, which promotes N2O production. It is likely that denitrification also dominates N2O production in tropical regions, but the dampened effect of N input on stimulating soil N2O emissions in these areas suggests that the loss of NO3− substrate due to intensive leaching might be an important issue. This study could provide a better understanding of the heterogeneous risks of soil N responses in different climatic zones in the context of increasing global N deposition.HighlightsLarger N input‐induced increases in soil NO3− concentrations in temperate regions may derive from increased nitrification.Larger N input‐induced increases in soil N2O emissions in subtropical regions may derive from increased denitrification.Less increase in soil N2O emissions in tropical regions after N input may be due to heavy precipitation‐induced NO3− leaching.Soil N2O emissions in subtropical regions may be more sensitive to increased N input compared to other climatic zones.