How Trees Talk Through Underground Fungal Networks | Science Explained

Mycorrhizal networks function like a vascular system for plants, extending root access from 1% to 10-15% of soil volume. Plants transfer 90% of photosynthetic sugars to fungi in exchange for nutrients. These networks transport water, minerals, and amino acids over distances of 10 meters or more. Mycorrhizal granules are visible structures that can be collected and stored for future use. This symbiosis is essential for plant nutrition in regenerative agriculture.

Mycorrhizal fungi form symbiotic relationships with plant roots, with endomycorrhizal fungi developing inside root tissues to exchange nutrients for sugars. Ectomycorrhizal fungi, found in natural forests but rarely in agricultural soils, create extensive underground networks connecting different plants. These networks function as an 'internet of the soil' enabling nutrient and chemical signal transfer between plants. Research demonstrates phosphorus can travel through these networks over 300 kilometers. This explains why leaving old olive trees in new plantations is beneficial—they maintain these networks and support new growth. The same principle applies to forest ecosystems where trees maintain their descendants through underground connections.

In agriculture, individual mycorrhizae can be cultivated and fields can be seeded with them on a large scale. But this cannot be done in forests - we must learn what nature does. We must think in terms of diversity - the more species of trees we plant, the more species of mycorrhizae will be in the soil, and we will create dense and complex networks that will make the forest more resistant and sustainable.

Forest soil transplanting involves adding a thin layer of healthy forest soil to degraded garden soil to restore biological activity. A 2016 study published in Nature Plants demonstrated that transplanting a soil layer less than 1 cm thick from grassland or heathland onto degraded farmland (chemically managed for nearly 60 years) restored the entire ecosystem within six years. The transplanted microbes restored plant communities, soil invertebrates, and fungal networks. A 2023 University of Wisconsin study found that trees inoculated with microbes from climate-matching sites had at least 50% higher survival rates under stress. Mycorrhizal fungi form symbiotic partnerships with approximately 80% of all land plants, extending root absorption capacity up to 100 times. A 2024 meta-analysis of 187 studies found these fungi increased phosphorus uptake by 105%, nitrogen uptake by 67%, and total plant biomass by 47%. Globally, mycorrhizal networks sequester 5 billion tons of carbon annually—equivalent to the combined annual emissions of the European Union and Russia.

Trees in forests communicate and support each other through underground fungal networks called mycorrhizae. These networks connect tree roots and allow nutrients and chemical signals to flow between trees. Even trees of different species and families participate in these support networks, sharing resources and potentially warning each other of dangers like insect attacks or drought.

Mycorrhizal networks can transmit signals about plant attacks to other connected plants. When one plant is attacked by herbivores, connected plants can receive these signals and activate their own defense systems. For example, when tomato plants are connected through mycorrhizal networks, damage to one plant causes other plants to produce defensive compounds. This 'warning system' allows plants to prepare defenses before being attacked. Plants have various defense mechanisms including thickening cell walls, depositing callose, forming cork tissues, and producing volatile compounds. Salicylic acid plays a key role in activating defense systems, and jasmonates are fundamental phytohormones associated with defense. Some plants have evolved to use these defense systems for attacking herbivores, as seen in carnivorous plants like the Venus flytrap.

Trichoderma harzianum, a cosmopolitan fungus, produces volatile organic compounds (VOCs) that mediate communication with plants, inducing growth promotion and inhibiting pathogen growth through specific signaling pathways involving NOX proteins (NOX1, NOX2, NOX3) and SKN7 transcription factor. The research demonstrates that NOX1 and NOX2 positively regulate volatile production for pathogen inhibition, while SKN7 negatively regulates it, with Metabolite 16 identified as a key compound responsible for the fungistatic activity against Rhizoctonia solani.

Plants use specific hormones for defense: salicylic acid against pathogens and jasmonic acid against herbivores. Salicylic acid, extracted from willow (Salix), is the basis for aspirin. It is produced through the shikimic acid pathway from phenylalanine. When infected, salicylic acid signals locally and systemically through phloem transport, and can be released as volatile compounds to warn neighboring plants. This signaling triggers defense responses throughout the plant.

Jasmonate is a plant hormone derived from cyclopentanone, playing crucial roles in biotic and abiotic defense responses. Biosynthesis occurs via the octadecanoid pathway: linolenic acid is oxygenated by lipoxygenase to form 13-HPOTrE, which cyclizes to OPDA in chloroplasts. OPDA is transported to peroxisomes via ABC transporters, where reduction by OPDA reductase and three cycles of beta-oxidation produce jasmonic acid. In the cytosol, jasmonate is conjugated with amino acids, glucose, or methylated to methyl jasmonate. Among conjugates, jasmonate-isoleucine is the most bioactive form orchestrating defense responses. Methyl jasmonate, first detected in jasmine petals, is volatile and serves as an inter-plant signaling cue. Catabolism converts jasmonates to 12-hydroxy derivatives via cytochrome P450 enzymes CYP94B3 and CYP94C1. Jasmonates are long-distance mobile signals, increasing throughout the plant within 2-5 minutes after wounding or herbivory, transported via xylem and phloem.

Trees communicate internally through sugars, amino acids, and gases traveling via vascular systems, coordinating activities between roots and leaves. Biologists define communication as capturing information signals and modifying behavior. Plants emit volatile organic compounds traveling centimeters to meters to inform other plant parts about threats. When attacked by herbivores, trees release jasmonate triggering defense cascades, producing toxins within 10-15 minutes. Electrical currents also spread through plant tissues, alerting other parts to threats. Trees function as supra-organisms hosting vast microorganism communities—a single oak hosts over 2,300 species. Plants and fungi have maintained symbiosis for 450 million years, with fungi helping plants absorb nutrients while receiving sugars.

Heavy machinery that compacts forest soil and chemical pesticides damage the underground fungal networks and root systems. These activities prevent forests from regenerating and make trees more susceptible to diseases.

Underground ecosystems face numerous threats despite receiving less attention than above-ground environments. Major threats include deforestation, desertification, over-application of industrial agricultural chemicals such as fungicides and fertilizers, and excessive plowing. Based on current trends, 90% of Earth's soils will be degraded by 2050 if these practices continue unchecked.

Human activities are causing massive declines in below-ground microbial biodiversity. Clear-cutting forests leads to massive declines in mycorrhizal fungi that form symbiotic relationships with tree roots. Intensive chemical agriculture with heavy tillage creates wildly different fungal and bacterial communities compared to organic or regenerative farming practices.

Human practices affecting soil are categorized as negative (causing degradation) and positive (preserving soil). Negative agricultural practices include: soil compaction from heavy machinery reducing water/air absorption and impairing root growth; salinization from groundwater evaporation and continuous flooding irrigation leaving salts in soil; and nutrient depletion from continuous monoculture depleting specific minerals. Negative industrial practices include: chemical contamination from petroleum facilities causing cancer risks; heavy metal contamination from industrial wastewater (lead, mercury); and nitrogen compound overuse from synthetic fertilizers causing health issues like blue baby syndrome.

Fungal networks face multiple threats from human activities including agricultural expansion, intensive land use changes, and chemical applications. Conventional agricultural methods using heavy fertilizers cause plants to stop feeding mycorrhizal networks since nutrients become readily available without fungal assistance. Tillage reduces network-forming fungi by approximately two-thirds and selects for fast-spore-producing fungi that don't form protective networks. Herbicides like Roundup can decrease spore viability by up to 70%. Logging removes trees that support fungal networks, potentially reducing abundance by 95%. Fire damages mycorrhizal communities, requiring decades for recovery. With UN projections indicating 90% of Earth's soils will show degradation by 2050, urgent conservation action is needed.