Arbuscular mycorrhizal fungi alleviate elevated temperature and nitrogen deposition- induced warming

Arbuscular mycorrhizal fungi alleviate elevated temperature and nitrogen deposition- induced 

warming potential by reducing soil N₂O emissions in a temperate meadow

Nitrous oxide (N₂O) is one of the most important greenhouse gases and plays an important role in global warming (IPCC, 2013). N₂O emissions contribute nearly 10% of anthropogenic climate warming because of their higher global warming potential. The emission of N₂O has been influenced by many global changes, including elevated temperature, drought, and nitrogen (N) deposition. Arbuscular mycorrhizal (AM) fungi form mutualistic associations with most terrestrial plants, which can help plant nitrogen (N) uptake and have also been shown to reduce soil N₂O emissions. However, the development and species community composition of AM fungi are influenced by warming and N deposition. To date, the mechanism by which warming, N deposition, and AM fungi interactively affect soil N₂O emissions in the field is still poorly understood.

Based on this, to fill research gap, a group of Chinese scientists from Institute of Grassland Science, Northeast Normal University established a 5-year experiment that included elevated temperature and N deposition combination with AM fungi suppression in a temperate meadow of the Songnen Plain (44°40′–44°44′ N, 123°44′–123°47′ E), located in western Jilin Province, China. Aiming to (1) study the influence of AM fungi on N₂O emissions under elevated temperature and N deposition; (2) assess the effects of elevated temperature and N deposition on the activities of nitrifying microbes; and (3) investigate the mechanism by which AM fungi reduce N₂O emissions under elevated temperature and N deposition.

The soil N₂O emissions were collected using a static chamber (20 cm × 20 cm × 40 cm) and measured by an analyzer (LGR 913–1054, Los Gatos Research, USA) during the rapid growth season of mid-July from 2015 to 2019. Moreover, the authors measured soil NH₄⁺-N and NO₃^--N, soil microbial biomass carbon (C) and nitrogen (N), AM fungal spore density and hyphae length density, the soil humidity and temperature and conducted soil DNA extraction and real-time quantitative PCR.

[Results]:

Effects of benomyl addition on soil N₂O emissions under elevated temperature and N deposition. C, control; T, elevated temperature; N, N deposition; TN, elevated temperature plus N deposition; B, benomyl addition.

Structural equation modelling results showing the pathways through which elevated temperature, N deposition, and benomyl addition affect soil N₂O emissions and their standardized path coefficients (χ2 = 148.39, P = 0.91; Akaike information criteria (AIC) = 240.38). Black arrows represent positive paths, and red arrows represent negative paths.

[Conclusion]:

The authors concluded that elevated temperature and N deposition alone and their interactions increased soil N₂O emissions in the Songnen meadow ecosystem. AM fungi reduced soil N₂O emissions under elevated temperature and N deposition. The AM fungal effect on N₂O emissions under elevated temperature was lower than that of N deposition. Under elevated temperature, the effect of AM fungi on soil N₂O emissions was mainly determined by the abundance of functional genes, while the influence of AM fungi on soil N₂O emissions was mainly determined by soil microbial biomass carbon under N deposition. These results indicate that although AM fungi can reduce soil N₂O emissions, the pathways by which AM fungi regulate soil N₂O emissions might vary under different global changes. The results highlight the negative effect of AM fungi on soil N₂O emissions under elevated temperature and N deposition and show that the influence of AM fungi on N₂O emissions might be simultaneously determined by global changes and ecosystem types. Predicting the potential role of AM fungi in reducing N₂O emissions under the conditions of nitrogen deposition and elevated temperature can contribute important insights and may provide a theoretical basis for the management and protection of grassland ecosystems under the background of future global climate change.