Symbiotic soil fungi mitigate nitrogen-driven methane emissions in an experimental grassland

Methane (CH₄) emission is a critical natural process contributing to atmospheric greenhouse gas accumulation and constitutes an important component of global carbon cycling. Arbuscular mycorrhizal (AM) fungi play vital roles in regulating greenhouse gas emissions and participate in soil carbon cycling. However, the understanding of the functions and regulatory patterns of AM fungi in regulating soil CH₄ emissions remains equivocal, particularly under non-waterlogged conditions accompanied by increased nitrogen (N) deposition. To fill this critical knowledge gap, this study dynamically monitored soil CH₄ fluxes spanning three plant growth seasons of the presence/absence of AM fungi under increased N deposition in an experimental grassland. The study found that increased N deposition stimulated soil CH₄ emissions, but this response was only detected in the absence of AM fungi. AM fungi exhibited a significant association with soil CH₄ emissions, and these correlative patterns were dependent on N deposition levels. Specifically, AM fungi significantly mitigated the stimulatory effects of high N deposition on CH₄ emissions, but AM fungi were correlated with elevated soil CH₄ emissions under low N deposition, likely in association with higher plant community diversity. Furthermore, plant community Shannon-Wiener diversity acted as a key factor that was interactively modulated by increased N deposition and AM fungi, showing a statistical association with soil CH₄ emissions. These findings provide experimental evidence that AM fungi are involved in regulating soil CH₄ emissions in an N deposition-dependent manner, and further highlight the close statistical linkage between plant community diversity and soil CH₄ emissions. Meanwhile, these results underscore the necessity of future study to quantify changes in soil microbial communities associated with CH₄ production and oxidation processes induced by AM fungi, contributing to informing evidence-based policies for mitigating global warming and ensuring sustainable ecosystem management under ongoing climate change.