[Denitrification and Anaerobic Ammonium Oxidation in Soil Nitrogen Migration Process in a Farmland of Wanshandang Lake].

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.

[Insight into the Process of Mn-ANAMMOX in Soils of Agricultural Drainage Ditches].

Anaerobic ammonium oxidation mediated by MnO2 (termed Mn-ANAMMOX) is a newly discovered microbial nitrogen removal pathway. However, few studies have reported on the Mn-ANAMMOX process and related microbial communities in agricultural drainage ditches. In this study, Mn(Ⅳ)-reducing bacteria (MnBR) enrichment cultivation was carried out for 340 days and an isotope tracing technique and high-throughput sequencing technology were used to provide convincing evidence of the occurrence of Mn-ANAMMOX. The results showed that simultaneous NH4+ oxidation and MnO2 reduction occurred during the reaction, and the production of NO2-, NO3-, 30N2, and Mn2+ was detected. Additionally, the average Mn-ANAMMOX rate, ammonium removal rate, and total nitrogen removal rate were 2.88 mg·(kg·d)-1, 20%, and 15%, respectively. Moreover, high-throughput sequencing results showed that after 340 d in the enrichment cultivation experiments, the abundance of MnBR increased from 27% to 70% at the phylum level, and the major genera of MnBR were determined as Acinetobacter and Geothrix, with relative abundances of 26.63% and 4.07%, respectively. Overall, the occurrence of Mn-ANAMMOX was directly proven during the MnBR enrichment cultivation experiments, and it might play an essential role in the pathway of microbial nitrogen removal.

[Insight into the Mechanism of Feammox in the Surface Soils of a Riparian Zone].

Anaerobic ammonium oxidation coupled to iron (Ⅲ) reduction (termed Feammox) is a recently discovered pathway of nitrogen cycling. However, little is known about the pathways of N transformation via the Feammox process in riparian zones. In this study, evidence of Feammox in the riparian zone soil layers (0-20 cm) was demonstrated using the isotope tracing technique and a high-throughput sequencing technology. The results showed that Feammox occurred in the riparian zones in four different soil layers (A:0-5 cm, B:5-10 cm, C:10-15 cm, D:15-20 cm) and the Feammox rates ranged from 0.25 mg·(kg·d)-1 to 0.29 mg·(kg·d)-1. In the B soil sample, the Feammox rate was significantly higher than in the other soil samples (P<0.05). In addition, iron reducing bacteria played an essential role in the Feammox process, and Anaeromyxobacter and Geobacter were detected in all the soil samples. In the B soil sample, the abundance of iron reducing bacteria was significantly higher than in the other soil samples (P<0.05). Overall, the co-occurrence of ammonium oxidation and iron reduction suggest that Feammox can play an essential role in the pathway of nitrogen removal in riparian zones.