Elucidating the Role of Bacterial and Arbuscular Mycorrhizal Fungi Inoculants in Mitigating Nitrous Oxide (N2O) Emissions in Agroecosystems Under Climate Change

Nitrous oxide (N2O) is a greenhouse gas that has a global warming potential approximately 300 times that of carbon dioxide (CO2). It is largely produced in agricultural soils through nitrification and denitrification processes driven by specific microbial functional genes (e.g., amoA, nirS, and nirK), which represent the main source of its emissions. The intensive use of nitrogen fertilizers increases nitrogen surplus in the ecosystem. This in turn accelerates the risk of nitrogen loss through leaching and volatilization, while also accelerating microbial pathways that drive N2O emissions in the soil. This issue raises severe environmental concerns within the context of global climate change, particularly through the climate-driven escalation of soil salinity, which further alters the microbial community and increases these emissions. Microbial inoculants, including bacteria and arbuscular mycorrhizal fungi, provide eco-friendly biological solutions to mitigate N2O emissions from agricultural soils. These inoculants could restore nitrogen balance in the soil by several strategies, such as improving nitrogen use efficiency, competing with native nitrifiers, and upregulating nosZ gene expression. This review highlights the current developments in the utilization of microbial inoculants for N2O mitigation, focusing on key bacterial genera (e.g., Bradyrhizobium, Dyadobacter, Stutzerimonas, Paenibacillus, and Bacillus) and arbuscular mycorrhizal fungi (AMF, e.g., Rhizophagus and Funneliformis), as well as the mechanisms used by these microorganisms. It also discusses the potential of using microbial inoculants in saline-affected soils, as well as the link between salinity and N2O emissions. Based on these insights, this review presents a thorough framework for the prospective use of microbial inoculants as an effective solution to sustainable agriculture while reducing the environmental hazards associated with N2O emissions, which endanger global food and climate systems.