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Global mycorrhizal fungi networks: untangling the wood wide web

Logo https://crowtherlab.pageflow.io/global-mycorrhizal-fungi-networks-untangling-the-wood-wide-web

Global mycorrhizal networks: untangling the wood wide web

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Forests are one of the world’s largest ecosystems and play a vital role in storing carbon and regulating the climate at a local, regional and continental scale by producing atmospheric moisture, rainfall and controlling temperature. In and around the tangled roots of the forest floor, fungi and bacteria grow with trees, exchanging nutrients through symbiotic relationships so that both can flourish. Yet, to fully understand the functioning of forest systems, we must understand this symbiotic soil microorganisms supporting their nutrient supply, their ability to sequester carbon and to withstand the impacts of climate change.  

Through a long-term collaboration with Stanford University, the Crowther Lab generated the first spatially explicit map of forest symbiotic status of mycorrhizal fungi. Similar to an MRI that helps to understand the functioning of the brain, this global map of fungal networks helps us understand the functioning of forest ecosystems and their reaction to climate change.
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Trees are not able to extract nutrients directly from the soil, but rather rely on symbiotic partnerships with mycorrhizal fungi or nitrogen-fixing bacteria to break down substances and transfer the released minerals. In return, trees provide fungi with energy in form of carbohydrates and in some cases protection from competitors. The most abundant symbiotic partners are mycorrhizal fungi. While arbuscular mycorrhizas penetrate the cells of their host’s roots, ectomycorrhizas surround the roots without penetrating them. 

In order to understand which type of mycorrhizal fungi dominates in which regions, and how their abundance can impact the success of forest restoration and conservation activities, we analysed 1.2 million forest inventory plots containing over 28,000 tree species around the world.
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For our research, we fed the location of trees from the forest inventory database along with information about what symbiotic fungi or bacteria most often associates with those species into an algorithm. With this, we were able to calculate the degree to which different variables such as climate, soil chemistry, vegetation and topography seem to influence the prevalence of each symbiosis. 

Additionally, training our models using these machine learning algorithms, we now have the first spatially explicit map of mycorrhizal fungi across the Earths’ forest systems.

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60% of the world’s trees are connected to adjacent trees by large networks of ectomycorrhizal fungi. Primarily these fungi prevail in high-latitude, temperate and boreal forests with a cold and dry climate. In contrast, lower latitudes with a-seasonal hot-and-wet climates are dominated by arbuscular mycorrhizae that enhance decomposition and promote rapid tree growth.
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We now know that nitrogen-fixing bacteria are probably limited by temperature and soil chemistry, whereas the two types of fungal symbioses are heavily influenced by variables that affect decomposition rates, such as temperature and moisture. Given that there is a significant difference between the nutrient cycling of forests dominated by each type of mycorrhizal fungi and that ectomycorrhizal networks are much more responsive to climate change, these high latitudes ecosystems are far more vulnerable and easily affected. 

If human carbon emissions continue unabated to 2100, our results show a 10 percent reduction in the world’s ectomycorrhizal fungi. As these fungi facilitate the uptake of carbon into the soil, these could cause a feedback loop which ultimately increases atmospheric carbon levels.
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