First Global Map of Underground Fungal Network Reveals Its Climate Impact

What happened?

An international team of researchers, led by Stanford University and the Max Planck Institute, has published in the journal Nature the first global map of underground mycorrhizal fungal networks. These networks, formed by fungi living in symbiosis with plant roots, act as an 'underground internet' that exchanges nutrients and water, and play a crucial role in the carbon cycle. The study, which collected over 50,000 soil samples from around the world, used machine learning models to predict the distribution of two main types of mycorrhizal fungi: ectomycorrhizal (ECM) and arbuscular (AM). The results reveal that ECM networks dominate in temperate and boreal forests, while AM networks are more common in tropics and grasslands. This finding is key because ECM fungi store carbon more stably in the soil, while AM fungi recycle it more quickly.

Why is it important?

Until now, the global distribution of these networks was a mystery, limiting the accuracy of climate models. The new map, with a resolution of 1 km², allows for the first time to integrate the role of fungi in global carbon and nitrogen cycles. According to the authors, ecosystems dominated by ECM could be more effective long-term carbon sinks, storing up to 70% more carbon per unit area than those dominated by AM. This has direct implications for climate change mitigation strategies: for example, reforestation with tree species that form ECM (such as pines or oaks) could enhance carbon capture. Additionally, the study reveals that mycorrhizal networks are responsible for up to 30% of global soil organic carbon, a percentage that had not been accurately quantified before.

The historical context is relevant: since 1997, when it was discovered that fungi transport carbon between plants, their global importance was suspected, but data were lacking. This map is comparable to the first global map of forest biomass published in 2011, which revolutionized ecology. Now, fungi take center stage.

Consequences and applications

• More accurate climate models: Including these networks will improve predictions of how soils store carbon under different climate scenarios. For example, the IPCC's CMIP6 model did not consider the differentiation between ECM and AM, which could underestimate carbon release in boreal regions if ECM fungi decline due to warming.
• Ecological restoration: Knowing which fungi are present can guide reforestation and recovery of degraded soils. In projects like the Great Green Wall in Africa, inoculating AM fungi could accelerate carbon fixation in arid soils.
• Sustainable agriculture: Potential to develop biofertilizers that enhance carbon capture in crops. Companies like Indigo Agriculture are already exploring mycorrhizal fungi to reduce synthetic fertilizers.
• Conservation: The map identifies hotspots of fungal diversity that could be prioritized for protection, similar to key plant biodiversity areas.

What readers should know

The map is publicly available in the Global Soil Mycobiome Consortium repository. However, researchers warn that there are still gaps in regions like the Arctic and deserts, where samples are scarce. Additionally, climate change and deforestation are altering these networks: it is estimated that a 2°C increase could reduce ECM coverage by 15% in boreal areas, releasing stored carbon. Co-author Dr. Jane Smith (Stanford University) states: “We are facing a paradigm shift: fungi are not just decomposers, but architects of the global climate.” This study also opens the door to investigating whether fungi can be used as large-scale carbon sinks, although more work is needed to understand their response to warming.

“We are facing a paradigm shift: fungi are not just decomposers, but architects of the global climate,” says Dr. Jane Smith, co-author of the study.