New research by Michela Audisio, PhD candidate at Göttingen University, Germany.
There is much more to trees than we see aboveground, and their interactions with fungi belowground are vital for their survival. Trees rely on the symbiotic interaction with specialized soil fungi to take up important resources such as nutrients and water. In exchange for this service, the fungi (also known as “mycorrhizal fungi”) receive sugars produced by the host tree via photosynthesis. In temperate forests, trees mainly form ectomycorrhizas, where the fungi colonize their roots but remain confined outside of plant cells. Ectomycorrhizas are easily recognized because the fungus produces a hyphal mantle that covers the root tip, giving a swollen appearance. Different fungal species colonizing the tree root also result in a multitude of shapes and colors of the mycorrhizal root tips.
Unfortunately, this precious mycorrhizal symbiosis is threatened by the perturbation of forest soil. Changes in the community composition of mycorrhizal fungi and species loss after drought and high nitrogen deposition have been reported by many studies, with anthropogenic climate change as the cause. But the dynamics of these impacts are not clear. Moreover, we don’t know if all forests respond the same way. For example mixed forests, where two or more tree species are growing together, might host more diverse fungal communities and mitigate the negative effects of climate change on soil communities and ecological processes.
In my experiment, I investigated how the mycorrhizal symbiosis is impacted by water scarcity and excessive nitrogen supply in different tree species combinations. By counting the relative proportion of vital mycorrhizal, dead, and non-mycorrhizal root tips under the microscope, I found that the fraction of dead root tips increases dangerously when trees are exposed to reduced watering and high nitrogen fertilization, already after one growing season. This effect was sometimes accompanied by a reduction of tree biomass. For different tree species, having a different tree neighbor made a difference in terms of mitigating the negative impacts.
This study was carried out with juvenile trees; therefore, the results need to be confirmed with mature trees in the forests. However, from this study we can learn that looking belowground is important to study (and prevent) the impacts of climate change and human activities. Mycorrhizal roots quickly react to changes in water and nitrogen availability, with potential consequences on the uptake of nutrients and growth of trees. This effect was not equal for all tree species. Knowing which tree species combinations are less impacted, can help us to better plan and manage the forests of the future.
Learn more about Michela Audisio’s work here.
Reference
Audisio, M., Sennhenn-Reulen, H., Schott, I. et al. Mycorrhization, root tip vitality and biomass of Fagus sylvatica, Picea abies and Pseudotsuga menziesii in monospecific and mixed combinations under water reduction and nitrogen addition. Trees (2024). https://doi.org/10.1007/s00468-024-02509-6
Plant Life Belowground 