Threats to Mycorrhizal Fungi

Mycorrhizal fungi are an essential part of the Earth’s ecosystems. These ancient organisms form a symbiotic relationship with plants, helping them absorb water and nutrients from the soil. In return, the plants provide the fungi with carbon. This mutually beneficial relationship is crucial for the health of belowground ecosystems. Unfortunately, mycorrhizal fungi face numerous threats. Disruption of mycorrhizal networks can disrupt the aboveground ecosystems they support.

A Staggering 59% of All Planetary Biodiversity is Estimated to be Underground. Yet this hidden diversity is often ignored.

Recent research estimates that 59% of all biodiversity on the planet lives below ground. By not looking at threats to soil ecosystems, we're ignoring more than half of the biodiversity on the planet. Belowground biodiversity is critical to promoting soil health, promoting general ecosystem health, and it provides many of the services and natural resources that we rely on to form our global economies and to sustain human life.

Understanding Mycorrhizal Fungi

Before diving into the threats, it's important to understand what mycorrhizal fungi are and why they're so vital. There are two primary types: arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EcM). AMF penetrate the root cells of plants, while EcM form a sheath around plant roots. Total diversity estimates put AMF in the range of 300-1600 species, while EcM likely exceed 20,000 species on Earth.  Both types enhance the plant's ability to access nutrients like phosphorus and nitrogen, improving plant growth and resilience.

The Importance of Belowground Ecosystems

Belowground ecosystems, which include soil, roots, and microorganisms, play a critical role in maintaining plant health and ecosystem stability. Mycorrhizal fungi are a key component of these ecosystems, facilitating nutrient cycling and improving soil structure. They also help plants withstand environmental stresses such as drought and disease, making them indispensable for both natural and agricultural systems.

We Know More About Aboveground Biodiversity Than Underground Biodiversity

We don't know much about threats to underground biodiversity compared to what we know about threats to above ground biodiversity. It's obvious that if a forest is clear-cut and bird populations are tracked over time that their habitat has been dramatically reduced. It's proving a lot harder to understand and precisely measure belowground impact in terms of underground biodiversity or fungal biodiversity. 

Activities Directly Harmful to Mycorrhizal Fungi

There are very direct ways that we impact underground habitats at the expense of soil biodiversity and fungal biodiversity. These include physically disrupting the soil habitat with tillage or removal of plants (clear-cutting), compacting soil by driving heavy machinery over it, and directly applying chemical inputs, like pesticides and fungicides which can have a negative effect on the diversity and abundance of fungi. Below, we describe these in more detail.

Soil Disturbance

Activities such as construction, agriculture, and deforestation can severely disturb soil, damaging or destroying mycorrhizal networks. Soil compaction and erosion reduce the fungi's habitat, limiting their ability to colonize plant roots or build hyphal networks within soils.

Chemical Use

The use of chemical fertilizers and pesticides can harm mycorrhizal fungi. Excessive fertilizers can lead to nutrient imbalances, reducing the plant's reliance on mycorrhizal associations. Pesticides, particularly fungicides, can directly kill mycorrhizal fungi, disrupting their networks and the ecosystems they support. The direct application of chemical inputs that change the nutrient dynamics of systems that are naturally regulated by mycorrhizal fungi. Likewise, the application of pesticides, herbicides, or fungicides can have an extremely detrimental effect on the diversity and abundance of mycorrhizal fungi.

Pollution

Pollutants such as heavy metals and acid rain can negatively affect mycorrhizal fungi. These substances alter soil chemistry, making soils inhospitable for sensitive fungi and preventing them from forming symbiotic relationships with plants. But some mycorrhizal fungi even help plants tolerate heavy metal contamination. There is now growing interest to use these symbiotic fungi as a bioremediation tool for the millions of contaminated land sites covering 20 million hectares across the planet.

Indirect Threats to Mycorrhizal Populations

Examples of indirect activities which are harmful to underground mycorrhizal fungal biodiversity:

• Reducing habitat 
• Fragmented habitat
• Urbanization
• Climate change through temperatures shifts or droughts 
• Invasive plant or fungal species coming into a natural community 
• Shifts in forest tree species populations
• Habitat loss by the loss of their symbiotic, partner interaction. 
• Loss of habitat, 
• Disturbances 

Indirect threats can also impact mycorrhizal fungi by altering the environment in which they thrive. These threats include:

Climate Change

Climate change presents a significant threat to mycorrhizal fungi. Rising temperatures and changing precipitation patterns can alter soil conditions, affecting the survival and function of mycorrhizal networks. Additionally, climate change can lead to shifts in plant communities, impacting the availability of host plants for fungi. Across North America, pine forests might lose up to ¼ of their EcM species, and over ⅓ of tree-EcM symbioses are at risk due to climate change.

Habitat Loss

The destruction of natural habitats reduces the availability of suitable environments for mycorrhizal fungi. As forests, grasslands, and other ecosystems are converted for agriculture or urban development, the fungi lose essential habitats, leading to declines in their populations.

Invasive Species

Invasive plant species can disrupt native plant communities and their associated mycorrhizal networks. These invaders often form different types of mycorrhizal associations or none at all, altering nutrient cycling and reducing the resilience of belowground ecosystems.

What We Can Do to Protect Mycorrhizal Networks

Given the importance of mycorrhizal fungi to ecosystem health, it's crucial to take action to encourage, preserve and advocate for the protection of these networks.

Habitat Conservation

Conserving natural habitats is essential for the preservation of mycorrhizal networks. Protecting forests, grasslands, and other ecosystems ensures that fungi have the environments they need to thrive. Supporting reforestation and habitat restoration projects can also help rebuild damaged mycorrhizal networks.

Sustainable Agriculture Practices

Implementing sustainable agriculture practices can help protect mycorrhizal fungi. This includes: reducing tillage, minimizing chemical use, incorporating crop rotations These practices can help maintain healthy belowground ecosystems. Organic farming methods, which prioritize soil health and biodiversity, are particularly beneficial for mycorrhizal fungi.

Pollution Control

Reducing pollution is vital for the health of mycorrhizal fungi. Implementing policies to limit emissions of harmful substances and promoting sustainable waste management practices can help maintain soil quality and support mycorrhizal populations.

Research and Education

Continued research is needed to better understand the complex interactions between mycorrhizal fungi and their environments. By investing in scientific studies, we can develop more effective conservation strategies. Additionally, educating the public about the importance of mycorrhizal fungi can raise awareness and encourage actions that support their preservation.

Conclusion

Mycorrhizal fungi are vital components of belowground ecosystems, playing a crucial role in plant health and nutrient cycling. However, they face serious threats, both direct and indirect, that can disrupt their networks and the ecosystems they support. It's important to think about not only physical disruptions to soil environments, but all of the indirect things that are happening aboveground that might impact mycorrhizal fungi, like exposure to pollution, and increases in temperature. In many cases, scientists are observing that mycorrhizal fungi are sensitive to impacts such as loss of habitat, disturbances or climate change and urbanization.

We Need to Develop Tools for A Global Perspective on Where Threats to Underground Biodiversity Are Concentrated

We currently lack a global perspective on where both direct and indirect threats are most concentrated for underground biodiversity. We need to develop tools or analytical pipelines to help us pinpoint where the threats are most concentrated for underground biodiversity. We then need to monitor over time like we do for forest ecosystems with satellite monitoring. We have monitoring systems in place to look for biodiversity and habitat loss and aboveground, but we lack those similar tools and methods for belowground biodiversity,