Mycorrhizal Fungi and the “Wood Wide Web”

Modern forests are not just individual trees growing side by side — they are complex, interconnected networks of organisms, with mycorrhizal fungi playing a crucial role. These invisible underground networks, stretching for hundreds of meters beneath the surface, create the so-called Wood Wide Web — the forest’s natural communication and logistics system.

Mycorrhiza is a symbiotic relationship between fungi and plant roots, where both parties benefit:

• Fungi receive photosynthetic products from plants (primarily carbohydrates),

• Plants gain access to otherwise hard-to-absorb mineral nutrients (such as phosphorus and nitrogen) and improved hydration.

There are two main types of mycorrhiza:

Ectomycorrhiza – found mainly in temperate and boreal forests (e.g., birches, oaks, pines); fungi surround the plant roots, forming a characteristic “mantle” and penetrate between the root cells.

Endomycorrhiza (arbuscular mycorrhiza) – dominant in tropical regions and grasslands; fungal hyphae penetrate the interior of root cells.

“Wood Wide Web” – A Cooperative Forest

The concept of the Wood Wide Web was popularized by Dr. Suzanne Simard from the University of British Columbia. In the 1990s, her experiments demonstrated that trees can exchange not only water and nutrients but also carbon via the mycorrhizal network.

In one of her key experiments (Simard et al., Nature, 1997):

• Isotope-labeled carbon molecules (^14C) were used,

• Observations showed that pine trees transferred carbon to other trees via the fungal network.

It turned out that:

• Old, well-established trees supplied carbon to young seedlings growing in the shade, increasing their chances of survival,

• In stressful situations (e.g., lack of light or disease), plants could prioritize supporting “relatives” through the fungal network.

This discovery fundamentally changed our understanding of forest ecosystems: trees do not merely compete ruthlessly for resources — they often cooperate, forming complex communities.

The Role of Mycorrhizal Networks in Ecosystem Resilience

Mycorrhizal networks enhance forest resilience to climate change and disease because they:

• Enable the distribution of water during droughts,

• Accelerate plant adaptation to changing conditions,

• Strengthen resistance to pathogens (some mycorrhizal fungi produce natural antibiotics).

Research published in New Phytologist (Barto et al., 2012) showed that damage to mycorrhizal networks (e.g., through deforestation) significantly reduces biodiversity and the vegetation’s regenerative capacity.

Scientific curiosity:

Recent experiments show that even plants of different species (e.g., deciduous and coniferous trees) can exchange resources through shared fungal networks, suggesting the existence of multi-species “underground communities.”

Soil Microbiome and Plant Health

Although soil has long been seen primarily as a physical substrate for plants, modern research shows that it is, in fact, an active, biological “support ecosystem.”
The health of the soil microbiome directly impacts the health, growth, and resilience of plants — from rainforests to urban parks.

The Microbiome as Plants’ “Second Immune System”

Unlike animals, plants do not have a mobile immune system. Their defense against pathogens and environmental stress largely depends on cooperation with microorganisms inhabiting their roots — the so-called rhizosphere (the soil zone directly surrounding the roots).

Research shows that:

• Rhizospheric bacteria (e.g., from the genera Pseudomonas, Bacillus) can produce antibiotic compounds that inhibit the development of pathogenic fungi and bacteria (Weller et al., 2002, Phytopathology),

• Mycorrhizal fungi enhance plants’ ability to absorb water and minerals under stress conditions (e.g., during drought),

• Protists and nematodes regulate bacterial and fungal populations, preventing pathogen dominance.

Microbiome Diversity = Ecosystem Resilience

A rich and diverse soil microbiome operates on the principle of an “ecological insurance effect” — the more organisms performing similar functions, the greater the resilience to disturbances.
Research published in Nature Ecology & Evolution (van der Heijden et al., 2016) indicates that:

• The greater the diversity of microorganisms in the soil, the higher the plant productivity,

• Soils with impoverished microbiomes are more susceptible to pathogen invasions and degradation.

As in plant and animal ecosystems, complex microbial food webs promote stability.

Probiotics for Soil

In recent years, a new field called biofertilization has been developing, involving the introduction of beneficial microorganisms into the soil to improve plant growth and resilience.

Examples of such organisms include:

• Nitrogen-fixing bacteria (e.g., Rhizobium for legumes),

• Phosphate-solubilizing bacteria (releasing phosphorus from inaccessible mineral forms),

• Inoculant mycorrhizal fungi (now commercially available for forestry and agriculture).

Field experiments show that soil inoculation with probiotics increases crop yields, improves plant resistance to diseases, and reduces the need for chemical fertilizers and pesticides.

Changes in the Microbiome and Ecosystem Degradation

The soil microbiome is a dynamic system sensitive to environmental changes. Unfortunately, human activity over recent decades has led to dramatic disruptions of this hidden life network.
Changes in the composition and diversity of soil microorganisms have serious consequences — not only for plant health but also for entire ecosystems.

Soil Degradation: The Silent Crisis of the 21st Century

According to a report by the Food and Agriculture Organization (FAO, 2015), as much as 33% of the world’s arable land is degraded, mainly due to:

• Intensive monoculture farming,

• Overuse of chemical fertilizers and pesticides,

• Excessive tillage,

• Urbanization and surface sealing,

• Deforestation.

Each of these actions leads to:

• A reduction in the number and diversity of soil microorganisms,

• Disruption of natural nutrient cycles,

• A decrease in humus content,

• Erosion and desertification.

What Happens When the Soil Microbiome Dies?

Field studies have shown that degraded soils lose their ability to:

• Retain water,

• Sequester organic carbon,

• Support plant growth and ecosystem regeneration.

Example:
An analysis of soils from deforested areas of the Amazon (Rodrigues et al., PNAS, 2013) revealed that deforestation not only alters the physical structure of the soil but also causes a drop of over 60% in microbial diversity, with pathogenic or opportunistic organisms taking over.

Domino Effect:

• A destroyed microbiome = weaker plants, more susceptible to diseases and drought,

• Weaker plants = lower biomass and less organic matter returning to the soil,

• Less organic matter = further microbiome degradation,

• Resulting in — accelerated desertification, loss of biodiversity, and loss of carbon sequestration.

Urbanization and Soil: Permanent Microbiome Loss?

In cities, where soil is paved over or intensively used, its microbial life is almost completely destroyed.
Studies on “urban soils” (Pouyat et al., Urban Ecosystems, 2010) show that:

• Cities host 30–50% fewer microorganism species compared to natural soils,

• The functional structures of the microbiome are significantly simplified — urban soils lose functions related to nitrogen and carbon cycling.

This means that urban green spaces — parks, squares, pocket forests — must be carefully designed to restore soil life if they are to function as real “green lungs” of cities.