To explore the rate variation and contribution to N loss of denitrification and anaerobic ammonia oxidation (ANAMMOX) in the nitrogen migration process of farmland soils in southern China, we assess the physicochemical characteristics soil samples of different soil layers from farmland and different land use types (farmland, river channel, riparian zone, and lake sediment) in a wheat-rice rotation area of Wanshandang Lake. Illumina MiSeq sequencing and quantitative real-time polymerase chain reaction (qPCR) are used to investigate the microbial community composition and functional gene abundances of the samples. The potential denitrification and ANAMMOX rate (calculated by N2) of each sample was determined by an isotope culture experiment. It was demonstrated that the potential denitrification rate was significantly positively correlated with TOC, NH4+-N, and NO3--N (P<0.05), and with the abundances of nirS, nirK, and nosZ (P<0.05). The denitrification rate of surface soils was (11.51±1.04) nmol·(g·h)-1, which was significantly higher than other soil layers and other land use types (P<0.05). While the ANAMMOX rate in farmland soils was the highest in the 20-30 cm layer and reached (0.48±0.07) nmol·(g·h)-1. In addition, denitrification was the main cause of N loss in surface soils of the studied farmland, accounting for 91.9%-99.7% of overall loss, and ANAMMOX played an important role in the production of N2 in deep soils.
Keywords: anaerobic ammonia oxidation (ANAMMOX); contribution to N loss; denitrification; isotope tracing; nitrogen migration.