Nitrous oxide (N₂O) is one of the most important greenhouse gas causing global warming. At the same time, N₂O also participates in many photochemical reactions in the atmosphere, destroying the atmospheric ozone layer. Compared to the Carbon dioxide (CO₂) content in the atmosphere, the relative content of N₂O is much lower. However, its warming potential per unit mass is 298 times that of CO₂. In terrestrial ecosystems, soil is an important source for N₂O emissions. The N₂O in the soil mainly comes from the transformation of available nitrogen mediated by various microorganisms.

Arbuscular mycorrhizal (AM) fungus is a widely distributed soil fungus in terrestrial ecosystems, which can form a symbiotic relationship with more than 75% of plant roots. AM fungi can enhance the nutrient uptake of the host plant through its hyphae network, improve the host plant's stress resistance, and improve the physical and chemical properties of the soil. It is generally believed that AM fungi themselves do not have the saprophyte ability and are unlikely to be direct producers or consumers of N₂O, but AM fungi have the ability to absorb active nitrogen in the soil and interact with other soil microorganisms to affect the production of N₂O from the soil.

In order to better explore how AM fungi regulate the production and emission of N₂O from the soil, researchers from the Centre for Mountain Futures of the Kunming Institute of Botany, Chinese Academy of Sciences (KIB/CAS), based on indoor experiments, set up a microcosm experiment under controlled environment to address this knowledge gap. In this experiment, two independent soil environments were established, which were either allowed (AM) or prevented (NM) access by AMF hyphae. Soil physicochemical properties, N₂O flux, the diversity of bacterial communities, and the abundance of key genes responsible for N₂O production were assessed in both treatments over three months. The results showed that the presence of AMF significantly decreased N₂O emissions from agricultural soils in the 1st month, and the abundance of key genes responsible for denitrification (nirK and nosZ) significantly decreased in AM treatments, indicating that the regulation of N₂O emissions is transmitted by AMF-induced changes in the denitrification process. A structural equation model further revealed that AMF indirectly influenced N₂O emissions by altering the abundance of N metabolism-related genes, rather than by altering soil chemical properties or the diversity of bacterial communities. Thus, the research proposed a possible mechanism by which AMF can regulate denitrification activities and therefore N₂O emissions from agricultural soils.

The major results were published online under the title "Arbuscular mycorrhizal fungi potentially regulate N₂Oemissions from agricultural soils via altered expression of denitrification genes" in Science of The Total Environment. GUI Heng, an assistant researcher at the Kunming Institute of Botany, Chinese Academy of Sciences, is the first author of the paper, and Prof. XU Jianchu is the corresponding author of the paper. This work was funded by the Yunnan Fundamental Research Projects (grant no.: 2019FB063) and the National Natural Science Foundation of China (NSFC Grant 32001296).

Fig. 1 Graphical abstract of general design and major findings of this research.

Fig. 2 Structural equation model (SEM) demonstrating the possible effects of AM fungi on N2O emssion from the soil