Nitrification inhibitors affect the abundance of ammonia-oxidizing microorganisms and nitrification in black soil in a short-term microcosm

Abstract:

[Background] The black soil area in northeast China is an important grain production base in China. However, the excessive use of chemical fertilizer has caused serious environmental issues, including nitrogen loss and environmental pollution. Nitrification, one of the key steps in nitrogen cycling, is mainly driven by microorganisms. [Objective] To distinguish the relative contributions of ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and comammox to soil nitrification by using nitrification inhibitors 3,4-dimethylpyrazole phosphate (DMPP) and acetylene in the black soil fields with low and high nitrogen content. [Methods] The soil samples applied with no nitrogen fertilizer (low-nitrogen soil) and nitrogen fertilizer (high-nitrogen soil) were collected from the black soil area in the long-term fertilization experiment. The effects of nitrification inhibitors on soil available nitrogen content, the abundance of ammonia-oxidizing bacteria, and their relationship were investigated by quantitative PCR of soil microcosms. [Results] Ammonia-oxidizing archaea and comammox Clade B predominated in the low-nitrogen soil, while ammonia-oxidizing bacteria and comammox Clade A predominated in the high-nitrogen soil. Both nitrification inhibitors, DMPP and acetylene, significantly inhibited ammonia oxidation, with more pronounced effects in high-nitrogen soil. Acetylene had a greater inhibitory effect than DMPP on ammonia oxidation. In addition, acetylene significantly reduced the abundance of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and comammox Clade B in low-nitrogen soil, while DMPP significantly inhibited ammonia-oxidizing bacteria and comammox Clade A. The correlation analysis showed that the amoA abundance of ammonia-oxidizing bacteria and archaea was positively correlated with NO₃⁻-N content and negatively correlated with NH₄⁺-N content in low-nitrogen soil. However, the amoA abundance of ammonia-oxidizing microorganisms had no significant correlation with NH₄⁺-N or NO₃⁻-N content in high-nitrogen soil. [Conclusion] The long-term application of nitrogen altered the responses of ammonia-oxidizing microorganisms to environmental changes in black soil.