How do natural soil <scp> NH ₄ ⁺ </scp> , <scp> NO ₃ ⁻ </scp> and <scp> N ₂ O </scp> interact in response to nitrogen input in different climatic zones? A global meta‐analysis

Abstract

Abstract The increase of fossil‐fuel burning and nitrogen (N) fertilizer consumption continues to elevate global N deposition, leading to significant increases of soil NH 4 + and NO 3 − concentrations, and thus N 2 O 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 N 2 O emissions with soil NH 4 + and NO 3 − 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 NO 3 − 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 NH 4 + concentrations by N input is much less than soil NO 3 − concentrations, at 20%, 26% and 28% in temperate, tropical and subtropical regions, respectively. The significantly larger increase in soil NO 3 − concentrations but slightly lower increase in soil NH 4 + 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 NH 4 + to NO 3 − . Soil N 2 O 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 N 2 O production. It is likely that denitrification also dominates N 2 O production in tropical regions, but the dampened effect of N input on stimulating soil N 2 O emissions in these areas suggests that the loss of NO 3 − 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. Highlights Larger N input‐induced increases in soil NO 3 − concentrations in temperate regions may derive from increased nitrification. Larger N input‐induced increases in soil N 2 O emissions in subtropical regions may derive from increased denitrification. Less increase in soil N 2 O emissions in tropical regions after N input may be due to heavy precipitation‐induced NO 3 − leaching. Soil N 2 O emissions in subtropical regions may be more sensitive to increased N input compared to other climatic zones.

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