Journal article

Authors list: Gao, Wenlong; Fan, Changhua; Zhang, Wen; Li, Ning; Liu, Huiran; Chen, Xin; Liu, Yuqin; Wu, Xiaolong; Zhang, Jinbo; Müller, Christoph; Chen, Miao

Publication year: 2023

Journal: Soil Biology and Biochemistry

Volume number: 182

ISSN: 0038-0717

eISSN: 1879-3428

DOI Link: https://doi.org/10.1016/j.soilbio.2023.109046

Publisher: Elsevier

Abstract: 
In acidic paddy soils where crops with an ammonium (NH4+) preference are grown, ammonia (NH3) is largely transformed to NH4+, and organic nitrogen (N) is often too low to support organic nitrification, heterotrophic nitrifiers may have a preference for NH4+. If so, acidic paddy soils are likely a hotspot of heterotrophic NH4+ oxidation (OHNH4). To reveal if OHNH4 is active in acidic paddy soils, we investigated the existence of acetylene (C2H2)-resistant NH4+ oxidation at pH 5.4, 5.3, and 5.0 in paddy soils with 60% water holding capacity (WHC), using N-15 tracing and nitrification inhibition techniques (1.0% C2H2). As expected, C2H2-resistant NH4+ oxidation (0.0088 +/- 0.0012 mg N kg(-1) soil d(-1)) was detected in soils with a pH of 5.0. In the presence of 1.0% C2H2, increased N-15 in the NO3 pool under (NH4NO3)-N-15 labelling suggested the existence of C2H2-resistant NH4+ oxidizers. Through a concentration gradient experiment of C2H2 (0, 0.01%, 0.1%, and 1.0%) on the pH 5.0 soil, 0.01% C2H2 was found to be sufficient for complete inhibition of autotrophic nitrification, suggesting that NH4+ oxidation in samples receiving 0.1% or 1.0% C2H2 is unlikely driven by autotrophs. The trend toward higher rates when C2H2 increased from 0.01% to 0.1% suggested that, C2H2-resistant NH4+ oxidizers in paddy soils are likely carbon (C)-limited. The trend toward lower rates when C2H2 increased from 0.1% to 1.0% implied an inhibition in the high concentration. At 0.1% C2H2, the trend toward lower rates when soil moisture increased from 60%WHC to 100%WHC indicated that C2H2-resistant NH4+/NH3 oxidizers prefer drier conditions, and OHNH4 will be less active at flooded conditions. Since there is evidence of organic and inorganic N oxidation by heterotrophs are mutually exclusive, we thus used a N-15 tracing model to separate organic nitrification from inorganic nitrification to clarify that low OHNH4 in samples was irrelevant to heterotrophic nitrification of organic N (OHORG). In summary, isotopic evidence has been provided to suggest that OHNH4, although with a low rate, has the potential to proceed in acidic paddy soils. In which, low OHNH4 is unrelated to OHORG, and an exogenous C source is needed to activate heterotrophic NH4+/NH3 oxidizers.

Harvard Citation style: Gao, W., Fan, C., Zhang, W., Li, N., Liu, H., Chen, X., et al. (2023) Heterotrophic ammonium oxidation is not active in acidic paddy soils, Soil Biology and Biochemistry, 182, Article 109046. https://doi.org/10.1016/j.soilbio.2023.109046

APA Citation style: Gao, W., Fan, C., Zhang, W., Li, N., Liu, H., Chen, X., Liu, Y., Wu, X., Zhang, J., Müller, C., & Chen, M. (2023). Heterotrophic ammonium oxidation is not active in acidic paddy soils. Soil Biology and Biochemistry. 182, Article 109046. https://doi.org/10.1016/j.soilbio.2023.109046