N2O production pathways in the subtropical acid forest soils in China

To date, N₂O production pathways are poorly understood in the humid subtropical and tropical forest soils. A ¹⁵N-tracing experiment was carried out under controlled laboratory conditions to investigate the processes responsible for N₂O production in four subtropical acid forest soils (pH<4.5) in China. The results showed that denitrification was the main source of N₂O emission in the subtropical acid forest soils, being responsible for 56.1%, 53.5%, 54.4%, and 55.2% of N₂O production, in the GC, GS, GB, and TC soils, respectively, under aerobic conditions (40%–52%WFPS). The heterotrophic nitrification (recalcitrant organic N oxidation) accounted for 27.3%–41.8% of N₂O production, while the contribution of autotrophic nitrification was little in the studied subtropical acid forest soils. The ratios of N₂O–N emission from total nitrification (heterotrophic+autotrophic nitrification) were higher than those in most previous references. The soil with the lowest pH and highest organic-C content (GB) had the highest ratio (1.63%), suggesting that soil pH-organic matter interactions may exist and affect N₂O product ratios from nitrification. The ratio of N₂O–N emission from heterotrophic nitrification varied from 0.02% to 25.4% due to soil pH and organic matter. Results are valuable in the accurate modeling of N2O production in the subtropical acid forest soils and global budget.