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 N-15-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%WEPS). 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. Crown Copyright (C) 2011 Published by Elsevier Inc. All rights reserved.