Soil fungi and trees in changing environments

Soil is a part of the natural world that is both affected by and contributing to climate change. Soil is one of the largest sources of carbon in the world. It is primarily accumulated through plants which fix the carbon from carbon dioxide in the air; the soil then directly absorbs the carbon as the plants decay. Additionally, dead leaves and animals are broken down by microbes in the soil, and carbon is accumulated. In the forest ecosystem, tree growth largely depends on the nutrients available in the soil; and the transfer of carbon through roots to the soil regulates ecosystem processes.

This nutrient-carbon exchange is made possible by mycorrhizal fungi and tree mutualism. Two groups of mycorrhizal fungi associations are typically formed in forest trees: arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (ECM) fungi. With collaborators, we found that the EMF-associated trees migrate slower than the AMF-associated trees, in both contemporary and paleo forests (Lankau et al. 2015). We further examined the continental-scale distribution of tree-mycorrhizal associations in relation to soil carbon and nitrogen (Zhu et al. 2018). Our results suggest that AM and ECM trees have differential success along nitrogen fertility gradients, or that AM and ECM trees promote differences in cycling rates of carbon and nitrogen because of traits associated with nitrogen acquisition; both processes could lead to a self-reinforcing positive plant-soil feedback. Overall, the mycorrhizal guild could be an emerging functional trait that determines the resistance of forests to the changing environment.

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