Meta-analysis of bacterial inoculation for nitrous oxide mitigation in agriculture

The biological mitigation of nitrous oxide (N2O), a significant greenhouse gas, plays a crucial role in slowing global climate change. Using a meta-analysis approach, this study systematically integrated 257 data points from 34 independent studies to quantitatively assess the regulatory effects of bacterial inoculation on N2O mitigation across diverse agricultural environments. Our analysis revealed that environmental system emerged as the most critical factor determining mitigation effectiveness, leading us to focus on two contrasting incubation systems: soil-based and liquid culture environments, for which potential molecular mechanisms were explored through functional gene analysis and phylogenetic characterization. Results demonstrated that bacterial inoculation significantly reduced N2O cumulative emissions and enhanced reduction rates, with effects exhibiting pronounced environment-specificity: liquid culture systems achieved a mitigation extent of 68.3%, superior to the 42.9% observed in soil-based systems, with corresponding N2O reduction rates of 3.68 and 1.78 μmol·h−1·g−1, respectively. Environmental factor analysis revealed that bacterial inoculation in soil-based systems showed lower net N2O accumulation under microoxic conditions, with greater effectiveness in acidic environments and during medium-term cultivation; whereas liquid culture systems achieved rapid mitigation response under anoxic neutral conditions. Functional gene analysis revealed potential synergistic regulatory patterns of multiple metabolic pathways including denitrification, dissimilatory nitrate reduction, and nitrogen fixation, with the denitrification pathway likely playing a core mitigation role in both environment types. This study revealed the environment-specificity of N2O biological mitigation and identified Bradyrhizobium and Azospira as key functional genera in soil-based and liquid culture systems, respectively, providing scientific guidance for developing environment-specific microbial mitigation technologies.