Soil pH-dependent efficacy of DMPP in mitigating nitrous oxide under different land uses

The emission pathways and intensities of nitrous oxide (N2O) vary across land uses, and the efficacy of mitigation measures may also differ. To investigate the key factors influencing the effectiveness of the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) in mitigating N2O under various land use conditions, we collected ten pairs of soils from tea plantations and adjacent cultivated land for laboratory incubation. As a complementary study, we conducted a meta-analysis based on 261 pairs of observations from 40 incubation studies to investigate the determinants of soil N2O mitigation by DMPP and to validate our experimental results. Results of the incubation experiment showed that DMPP was significantly less effective in mitigating N2O in tea plantation soils (73%) than in cropland soils (82%). Soil pH is a key factor influencing DMPP efficiency under different land use conditions. The lower pH of acidic tea plantation soils resulted in lower abundance and activity of ammonia-oxidizing bacteria (AOB). Under these low pH conditions, heterotrophic nitrification became an important source of N2O emissions in acidic tea plantation soils. As DMPP primarily inhibits AOB, it was less effective against heterotrophic nitrification, which likely contributed to its reduced efficacy in tea plantation soils compared to cropland soils. Our meta-analysis further confirmed the critical role of soil pH in determining DMPP effectiveness. The effect of soil pH on DMPP efficacy was mainly attributed to its regulation of heterotrophic and AOB-derived nitrification. These findings suggest that the field efficacy of DMPP in N2O abatement in tea plantations requires further investigation. Given the significant contribution of heterotrophic nitrification to N2O emissions in strongly acidic tea plantation soils, alternative N2O mitigation strategies should be explored.