The Importance of Mycorrhizal Associations in Plant Health

Have you ever wondered how plants, even in the most nutrient-poor soils, manage to thrive?

The answer lies beneath the surface, at least in part with a complex network of symbiotic relationships known as mycorrhizal associations. This intricate web of life holds immense importance for our gardens, landscapes, and the environment. Understanding these associations can help us make informed decisions about how we care for our plants and the soil they grow in.

What are Mycorrhizal Associations?

Definition and Explanation of Mycorrhizal Associations

Mycorrhizal associations refer to the mutually beneficial relationship between certain types of fungi and the roots of most plant species. The term ‘mycorrhiza’ comes from the Greek words ‘mykes,’ meaning fungus, and ‘rhiza,’ meaning root.

These relationships are crucial for the growth and survival of both parties involved.

Types of Mycorrhizae

Mycorrhizae can be broadly classified into ectomycorrhizae, endomycorrhizae, and ericoid mycorrhizae, each type having its unique characteristics and preferred host plants.

Ectomycorrhizae

Ectomycorrhizae form a sheath, called a mantle, around the outside of the plant roots. They also penetrate the root tissue, forming a network of hyphae, which are tiny fungal filaments.

This type of mycorrhiza is mainly associated with trees, particularly in temperate and boreal forests. Some of the common host plants include pine, oak, spruce, and birch. Ectomycorrhizae help their host plants by improving nutrient uptake, particularly nitrogen and phosphorus, and enhancing resistance to pathogens.

Endomycorrhizae

Endomycorrhizae, also known as arbuscular mycorrhizae, penetrate the cells of the root tissue, forming complex structures called arbuscules.

These arbuscules increase the contact surface between the plant and the fungus, facilitating nutrient exchange. Endomycorrhizae are the most widespread type of mycorrhizal association, found in about 85% of plant families, including many crop plants like wheat, maize, and tomato. They play a vital role in phosphorus uptake, helping plants thrive even in soils with low phosphorus availability.

Ericoid Mycorrhizae

Ericoid mycorrhizae are found mainly in plants belonging to the Ericaceae family, including heathers, blueberries, and rhododendrons. These fungi penetrate the cells of short, fine roots, forming dense coils.

They play an important role in nutrient-poor environments, like acidic peatlands or nutrient-poor sandy soils, enabling their host plants to access nutrients that are otherwise unavailable. Ericoid mycorrhizae are particularly effective at breaking down organic matter into simpler forms that plants can absorb.

The Science Behind Mycorrhizal Associations

These associations work through a symbiotic relationship where the mycorrhizal fungi colonise the plant roots, extending their reach far into the soil through the mycorrhizal network, or “wood wide web.”

This enables the plant to access nutrients and water that would otherwise be out of reach. In return, the plants provide the fungi with carbohydrates derived from photosynthesis.

Importance of Mycorrhizal Associations

Mycorrhizal Organisms and Plant Health

The relationship between mycorrhizal fungi and plants goes beyond nutrient uptake. It also helps enhance plant health by improving resistance to diseases, mitigating the effects of environmental stresses, and promoting overall growth and productivity.

They’re part of a tree’s immune system, in a similar way to how we have our own microbiome of healthy bacteria and fungi.

Mycorrhizal Organisms and Soil Health

Beyond the direct benefits to plants, mycorrhizal associations play a positive role in maintaining soil health. They help improve soil structure, enhance its fertility, and promote biodiversity by creating a conducive habitat for other beneficial soil organisms.

Mycorrhizal Organisms and Environmental Sustainability

Understanding and harnessing the power of mycorrhizal associations can contribute significantly to sustainable gardening and landscaping practices. They can help reduce reliance on artificial fertilisers, promote soil conservation, and even play a role in climate change mitigation by aiding carbon sequestration in soils.

Encouraging Mycorrhizal Associations in the Garden

Creating optimal conditions

Creating the right environment for these associations to thrive involves maintaining healthy soil rich in organic matter, and planting plenty of plants – preferable in a polyculture with a variety of plant types rather than a monoculture with little biodiversity.

Purchasing Mycorrhizae

For gardens that have been devoid of life for some time, introducing commercially available mycorrhizae can help establish these beneficial relationships.

However, it’s important to use the right type of mycorrhizae for the specific plants in your garden. If you’re unsure, Google which type your plant forms bonds with.

Also consider the potential impacts on local soil biodiversity. By introducing new genetic material into the soil that hasn’t evolved as part of the ecosystem, you are changing the soil biology. Whether this effect is “positive” or “negative” on the endemic flora and fauna may not be as simple as it seems on the surface.

Protecting Mycorrhizal Associations: Practices to Avoid

Mycorrhizal associations are delicate and can be easily disrupted by certain gardening and landscaping practices. To maintain a healthy and thriving network of these beneficial fungi, there are several things you should avoid:

Excessive Tilling

While tilling can help aerate the soil and mix in organic matter, excessive or deep tilling can damage the intricate networks formed by mycorrhizal fungi. These fungi form extensive webs in the soil, and turning the soil over can break these connections, disrupting their ability to assist plants and favouring bacterial organisms.

Instead, opt for minimal tillage or no-till methods to preserve these underground networks.

Overuse of Chemical Fertilisers and Pesticides

High levels of certain nutrients, particularly phosphorus, can inhibit the formation of mycorrhizal associations. Over-reliance on chemical fertilisers can lead to nutrient imbalances in the soil and negatively affect these beneficial fungi.

Similarly, some pesticides can harm mycorrhizal fungi, particularly fungicides. Aim to use organic fertilisers and Integrated Pest Control (IPM) methods where possible, and always follow the recommended application rates if using chemicals.

If in doubt, avoid using chemicals altogether or hire a professional to apply them for you.

Planting Non-Mycorrhizal Plants

Not all plants form associations with mycorrhizal fungi. Some, like the cabbage family and beetroot, don’t interact with these fungi and can even hinder their growth.

This isn’t really something to avoid. More a reminder to research your plants to ensure they’re compatible if you’re planning to buy mycorrhizae.

Excessive Watering

While mycorrhizal fungi need moisture to survive and thrive, overwatering can lead to waterlogged soil and create conditions unsuitable for these fungi. It’s important to strike a balance in watering – maintaining enough moisture for the fungi and plant roots to absorb, but not so much that it drowns the fungi or leads to root rot.

Fungal root rot diseases like phytophthora thrive in waterlogged conditions, and may colonise your plant.

Soil Erosion

Erosion can strip away the upper layers of soil, where many mycorrhizal fungi reside. To prevent erosion, consider implementing practices such as mulching, planting cover crops, or creating windbreaks.

By avoiding these practices, you can help protect and nurture the mycorrhizal associations in your garden or landscape, promoting healthier plants, richer soils, and a more sustainable environment.

Daniel’s Wrap

Mycorrhizal associations are more than just a fascinating natural phenomenon. They hold the key to healthier plants, richer soils, and a more sustainable future.

So put down those fungicides, and look after that soil, because it is our greatest asset.