The ectomycorrhizae, which are fungi that live on the roots of most tree species around the globe, have a close relationship. They form a dense fungal network around fine roots that provides nutrients to the trees and protects them from pathogens. The fungi in return receive energy from the trees via photosynthesis, which is made up of carbohydrates. This mutualistic relationship has been known by scientists for many years.
However, there has not been a complete understanding of how ectomycorrhizal mushrooms influence the growth of mature trees or whole forests. While it has been long believed that the main factors influencing tree growth are physical factors like temperature, rainfall, and anthropogenic nitrogen, the effects of underground fungal communities has been difficult to quantify and overlooked.
Three times faster growth
Postdoc Mark Anthony, along with fellow members of the group headed by Tom Crowther (ETH Zurich Professor of Global Ecosystem Ecology), have made a significant change in this. They studied five of the most popular European forest trees and found that fungal communities were linked to greater tree growth variation than local climate conditions or anthropogenic nitrogen inputs. This study was published in the journal ISME.
Tree-fold increases in tree growth rate are correlated with differences in ectomycorrhizal fungal communities. This study’s lead author Mark Anthony says that the fungi provide an ecological explanation for tree growth differences compared to other factors like temperature and rainfall.
These trees are the fastest growing because ectomycorrhizal fungal community is highly adapted for extracting the inorganic nitrogen compounds ammonium, nitrate and soil from the soil and making them available to the trees. Inorganic nitrogen, which is found in many fertilizers, is the most beneficial form of nitrogen and is an excellent grow promoter for plants.
Forest trees grew slower when local ectomycorrhizal fungal communities were adapted to provide nitrogen from organic sources. This nitrogen can be found in ground-decomposing biomass. The fungi need to first produce enzymes that depolymerize the biomass in order to release it. This takes more energy for the fungi than simply tapping inorganic nitrogen in the soil, and it also costs trees more. The trees are left with less energy because the fungi that tap into organic nitrogen get their energy from their tree partners.
Identification of fungi and their functions
These new insights were gained when the researchers identified the ectomycorrhizal fungal species in soil samples from 137 European forest monitoring sites. To determine the function of each fungus within the forest ecosystem, they paired it with its complete sequenced genome. They then correlated the functions of the fungi with decades worth of tree growth data to determine the relationship between ectomycorrhizal and tree growth. The tree species that were investigated were the deciduous oak and beech, as well as conifers pines and spruce.
Inoculating tree seedlings using the ideal fungi
Future research as well as forestry will be influenced by the team’s findings. Researchers now know which fungi are best for trees and what properties they have that can help them grow faster or slower. This study will allow the forestry industry to inoculate specific woodlands with specific fungal communities to make a targeted change in tree growth.
It is a well-established practice to inoculate tree seedlings with fungi. Anthony states that Anthony’s research provides a solid scientific foundation for the practice and can improve it.
He envisions other applications that could be related to climate change or rapidly changing environmental conditions. A faster growth rate could be a way to absorb more carbon from the atmosphere. Global change has caused some trees to stop growing well in certain regions. To help these trees survive, new fungal partners may be needed.
Future climate will give you a survival advantage
Anthony states that fungal communities that use organic nitrogen may be beneficial for many tree species in the future. Because of the increasing temperatures and high CO 2 levels, this promotes plant growth. Trees use readily available inorganic nitrogen to grow faster. This causes them to deplete their nitrogen stores faster, which could lead to slower long-term growth. This contrasts with the fungal communities that use organic nitrogen. Organic nitrogen is much more plentiful in soil, but is harder to access. If the right fungi are chosen, they could help their tree partner to grow in the future by capturing organic nitrogen over the long-term.