Contrasting Responses of N2O Mitigation to Different Nitrification Inhibitors in Tea Plantation Soils

Tea plantations are a hot-spot source of nitrous oxide (N2O) emissions in the agricultural system. Using nitrification inhibitors (NIs) is a promising way to mitigate agricultural N2O emissions and has been widely tested in many croplands. However, the efficiency of different NIs and whether there are soil-specific effects are still unclear in tea plantations with typical acidic soil conditions. This study evaluated the effects of three widely used NIs, i.e., dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl) pyridine (Nitrapyrin), through a lab incubation trial, on the nitrification suppression, N2O emissions, and ammonia-oxidizing microbial communities in two tea plantation soils with contrasting physicochemical properties (pH and texture). During the 50-day incubation, the soil with a higher pH and coarse texture (TA) exhibited a four-times-higher apparent nitrification ratio (ANR) than the more acidic and clay soil (HZ). Nitrification inhibitor addition resulted in about a 60% and 80% reduction in the ANR in HZ and TA soils, respectively. During the entire incubation, ammonium sulfate (N) addition without NIs emitted N2O at 64.1 ± 1.2 and 61.5 ± 0.4 μg N kg−1 (mean ± standard deviation, and the same in the following text) in the HZ and TA soils, respectively. Compared with the N alone, the N2O mitigation efficiency of DCD, DMPP, and Nitrapyrin was 38.3% ± 0.4% (standard deviation), 33.8% ± 0.99%, and 36.5% ± 0.59% in the HZ soil and 94.1% ± 0.39%, 52.8% ± 1.05%, and 95.6% ± 0.65% in the TA soil, respectively. Nitrapyrin more effectively suppressed both ammonia-oxidizing archaeal (AOA) and ammonia-oxidizing bacterial (AOB) abundance, particularly in the acidic soil (HZ), where ammonia-oxidizing archaea dominate nitrification. These results revealed the pivotal role of soil properties in controlling NI efficiency and highlighted Nitrapyrin as a potential superior nitrification inhibitor for N2O mitigation under the tested conditions in this study.