Atmospheric N deposition drives high N₂O yields of nitrification in acidic Chinese forest soils

Abstract

To understand large-scale drivers of soil nitrification and community-specific N₂O yield in forest ecosystems, we collected five forest soils along a climatic gradient in China, differing in soil pH (4.07‒6.44) and atmospheric N deposition. We conducted oxic soil slurry incubations with inhibitors to infer potential nitrification rates and N₂O yields for ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and heterotrophic nitrification. The largest nitrification potential and N₂O accumulation rate were observed in the temperate, circum-neutral soil. (Sub)tropical soils with low pH had relatively small nitrification rates with an increased contribution of AOA and heterotrophic nitrification to ammonia oxidation and N₂O production. The smallest nitrification potential with largest apparent N₂O yield (6.97%) was found in the most acidic subtropical forest soil, which also had the highest atmospheric N deposition. Ammonia oxidation kinetics showed nitrite (NO₂^‒) accumulation, suggesting inhibition of nitrite oxidizing bacteria (NOB) which together with chemical conversion of nitrification intermediates can explain the high apparent N₂O yield of this soil. NO₂^‒ and NO₃^‒ production did not balance NH₄⁺ consumption by autotrophic nitrification, strongly suggesting that acidic soils with high N deposition in subtropical China are a hotspot for nitrification-driven gaseous N loss, a substantial share of which emits as N₂O. These findings highlight the need to incorporate N saturation status and microbial community dynamics into global models of forest N cycling and to refine N management strategies in regions experiencing high atmospheric N deposition.

Graphical abstract

Keywords

nitrification potential / nitrous oxide yield / forest soil / AOA / AOB / N deposition

Highlight

	● The nitrification and N2O yield in forest soils varying in soil pH and N deposition were studied.
	● The temperate, neutral soil showed largest nitrification potential and N2O production.
	● Contributions of AOA to nitrification and N2O production increased with soil acidity.
	● N deposition acidified subtropical soils, leading to the largest apparent N2O yield.
	● Chemical conversion of intermediates in acid condition explains such a high yield.

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