Arbuscular mycorrhizal fungi offset NH emissions in temperate meadow soil under simulated warming and nitrogen deposition.

Most soil ammonia (NH) emissions originate from soil nitrogen (N) that has been in the form of exchangeable ammonium. Emitted NH not only induces nutrient loss but also has adverse effects on the cycling of N and accelerates global warming. There is evidence that arbuscular mycorrhizal (AM) fungi can alleviate N loss by reducing NO emissions in N-limited ecosystems, however, some studies have also found that global changes, such as warming and N deposition, can affect the growth and development of AM fungi and alter their functionality. Up to now, the impact of AM fungi on NH emissions, and whether global changes reduce the AM fungi's contribution to NH emissions reduction, has remained unclear. In this study, we examined how warming, N addition, and AM fungi alter NH emissions from high pH saline soils typical of a temperate meadow through a controlled microscopic experiment. The results showed that warming significantly increased soil NH emissions, but N addition and combined warming plus N addition had no impact. Inoculations with AM fungi strongly reduced NH emissions both under warming and N addition, but AM fungi effects were more pronounced under warming than following N addition. Inoculation with AM fungi reduced soil NH-N content and soil pH, and increased plant N content and soil net N mineralization rate while increasing the abundance of ammonia-oxidizing bacterial (AOB) gene. Structural equation modeling (SEM) shows that the regulation of NH emissions by AM fungi may be related to soil NH-N content and soil pH. These findings highlight that AM fungi can reduce N loss in the form of NH by increasing N turnover and uptake under global changes; thus, AM fungi play a vital role in alleviating the aggravation of N loss caused by global changes and in mitigating environmental pollution in the future.