pH-dependent microbial responses drive nitrous oxide mitigation by the nitrification inhibitor DMPP.

Nitrous oxide (N₂O) emissions from agricultural soils are a major environmental concern, largely driven by microbial nitrogen (N) transformations following fertilizer application. Nitrification inhibitors such as 3,4-dimethylpyrazole phosphate (DMPP) offer a promising strategy to mitigate these emissions, though their effectiveness is highly context-dependent. We conducted a laboratory microcosm experiment using four Cypriot soils spanning acidic to near-neutral pH to compare N₂O emissions, inorganic N dynamics, and N-cycling microbial communities under three treatments: (i) untreated soil (control), (ii) soil with commercial N-P-K fertilizer, and (iii) soil with a commercial N-P-K fertilizer containing DMPP. The inclusion of DMPP in fertilizer reduced cumulative N₂O emissions by 81%-96% in near-neutral soils, primarily through suppression of ammonia-oxidizing bacteria, with minimal effects on ammonia-oxidizing archaea. In acidic soil, however, DMPP failed to significantly alter emissions or microbial gene abundances. Multivariate analyses and machine learning models identified soil pH, NH4⁺ availability, and ammonia monooxygenase (amoA) gene abundance as key predictors of DMPP efficacy and N₂O fluxes. These findings underscore the critical role of soil properties particularly pH in determining inhibitor performance and highlight the need for site-specific N management strategies to optimize fertilizer use and mitigate greenhouse gas emissions.