Biological and chemical nitrification inhibitors exhibited different effects on soil gross N nitrification rate and N2O production: a 15N microcosm study

Nitrification inhibitors (NIs) are considered as an effective strategy for reducing nitrification rate and related environmental nitrogen (N) loss. However, whether plant-derived biological NIs had an advantage over chemical NIs in simultaneously inhibiting nitrification rate and N2O production remains unclear. Here, we conducted an aerobic N-15 microcosmic incubation experiment to compare the effects of a biological NI (methyl 3-(4-hydroxyphenyl) propionate, MHPP) with three chemical NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), dicyandiamide (DCD), and 3,4-dimethylpyrazole phosphate (DMPP) on (i) gross N mineralization and nitrification rate and (ii) the relative importance of nitrification and denitrification in N2O emission in a calcareous soil. The results showed that DMPP significantly inhibited m(_gross) rate (P < 0.05), whereas DCD, nitrapyrin, and MHPP only numerically inhibited it. Gross N nitrification (n(_gross)) rates were inhibited by 9.48% in the DCD treatment to 51.5% in the nitrapyrin treatment. Chemical NIs primarily affected the amoA gene abundance of ammonia-oxidizing bacteria (AOB), whereas biological NIs affected the amoA gene abundance of ammonia-oxidizing archaea (AOA) and AOB. AOB's community composition was more susceptible to NIs than AOA, and NIs mainly targeted Nitrosospira clusters of AOB. Chemical NIs of DCD, DMPP, and nitrapyrin proportionally reduced N2O production from nitrification and denitrification. However, the biological NI MHPP stimulated short-term N2O emission and increased the proportion of N2O from denitrification. Our findings showed that the influence of NIs on gross N mineralization rate (m(_gross)) was dependent on the NI type. MHPP exhibited a moderate n(_gross) inhibitory capacity compared with the three chemical NIs. The mechanisms of chemical and biological NIs inhibiting n(_gross) can be partly attributed to changes in the abundance and community of ammonia oxidizers. A more comprehensive evaluation is needed to determine whether biological NIs have advantages over chemical NIs in inhibiting greenhouse gas emissions.