Dissimilatory nitrate reduction to ammonium dominates nitrate reduction in long-term low nitrogen fertilized rice paddies. (April 2019)

• Record Type: Journal Article
• Authors: Pandey, Arjun; Suter, Helen; He, Ji-Zheng; Hu, Hang-Wei; Chen, Deli
• Is Part Of: Soil biology and biochemistry. Volume 131(2019)
• Page Start: 149
• Page End: 156
• Publication Date: 2019-04
• Subjects: Nitrogen fertilization -- DNRA -- Denitrification -- N2 fixation -- Gene abundance; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2019.01.007
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Dissimilatory nitrate reduction to ammonium (DNRA) and diazotrophic N2 fixation contribute to nitrogen (N) supply in rice paddies, whereas denitrification contributes to N loss. Continuous N fertilization in rice paddies is known to increase denitrification and reduce N2 fixation, however little is known about its effect on DNRA and the NO3 − partitioning between DNRA and denitrification. Here, we investigated the rates of DNRA, denitrification and N2 fixation, and their relevant microbial gene abundances, in long-term high and low N fertilized rice paddies using a 15 NO3 − tracer, an acetylene reduction assay and quantitative PCR analysis, in laboratory incubation studies. We observed that DNRA exceeded denitrification by a factor of eight in low N fertilized rice paddies, while DNRA was almost half of the denitrification rate in high N fertilized rice paddies. The nrfA gene abundance, related to DNRA, was significantly higher in the low N fertilized rice paddies and was positively correlated with DNRA rates. However, no clear difference in denitrifying gene ( narG, nirK and nosZ ) abundances was observed between the N fertilization regimes. The proportion of total NO3 − reduced by DNRA had a significantly positive correlation with the soil organic carbon-to-NO3 - ratio and negative correlation with the soil NO3 − concentration. N2 fixation added ten times more N in the low N input than in the high N input paddies. Our findings highlight the self-regulated microbial N cycling in low N input paddy systems which maintain long-term paddy soil N nutrition. Highlights: N2 fixation added ten times more N to low N input than to high N input rice paddies. DNRA retained the majority of nitrate in long-term low N input rice paddies. Denitrification dominated nitrate reduction in long-term high N input rice paddies. High SOC:NO3 − ratio favours NO3 − partitioning to DNRA in NO3 − limited paddy soils.