Underground Warnings: How Fungi Shape Plant Communication and Defense

Beneath our feet, a vast and silent communication network pulses with life. Dubbed the "wood wide web," this intricate web of fungi and plant roots connects entire forests, enabling trees and plants to share nutrients, information, and, as some believe, even warnings about danger.

But a new study published in Proceedings of the National Academy of Sciences (PNAS) asks a provocative question: Are plants really warning each other when attacked—or are fungi doing the talking?

Researchers from the University of Oxford and Vrije Universiteit Amsterdam have used evolutionary modeling to challenge long-standing assumptions about plant signaling. Their findings suggest that active altruistic communication between plants may be rare, and that fungi might play a more central, strategic role than previously thought.

Do Plants Really “Warn” Each Other?

When a plant is attacked by herbivores or pathogens, neighboring plants sometimes react—by boosting their chemical defenses, for instance. This has led scientists and the public to imagine a sort of botanical camaraderie: wounded plants sending alerts to nearby allies via underground fungal networks.

However, from an evolutionary standpoint, such generosity seems puzzling.

“Helping a competitor survive makes little sense unless there’s a benefit to the sender,” the study’s authors argue.

The key question: Is this plant-to-plant warning behavior truly intentional, or is it a byproduct of other processes like passive cues or fungal intervention?

The Science Behind the Theory: Modeling Plant-Fungal Communication

To unpack this mystery, the researchers built evolutionary mathematical models to test three main mechanisms of communication in plant-fungal networks:

1. Active signaling by attacked plants
2. Involuntary cues (uncontrolled signals that escape due to stress or energy loss)
3. Fungal monitoring, where fungi detect plant stress and relay it to others

These models considered factors like:

• The cost of signaling for the plant
• The competitive dynamics among neighboring plants
• The relatedness between plants in a network
• How signals (or cues) affect the fitness of each organism involved

The goal: identify which behaviors would be evolutionarily stable (i.e., persist across generations).

Key Findings: Fungi Take the Lead

1. Active Plant Signaling Is Rarely Evolutionarily Stable

Helping other plants by actively signaling danger provides no direct benefit to the sender. In fact, it improves the survival of competitors—a clear evolutionary disadvantage.

“Altruistic signaling in this context is almost never a winning strategy,” the authors explain.

2. Involuntary Cues Make More Sense

When under attack, plants may emit signals they cannot suppress—like biochemical “leaks” caused by stress or resource depletion. These cues, although not deliberate, can still trigger defensive responses in neighboring plants.

This suggests that what looks like communication may just be eavesdropping.

3. Fungi as Intelligent Middlemen

A more plausible scenario is that fungi monitor their plant partners for signs of distress—such as decreased photosynthesis or nutrient flow—and then transmit warnings to nearby hosts.

This benefits the fungus, which relies on the survival of multiple plants in its network. By keeping all partners healthy, the fungus maximizes its own fitness.

“The fungi act like underground sentinels,” the authors suggest. “They detect problems and quietly alert others.”

Implications for Ecology and Agriculture

Resilient Forests and Farms

If fungal networks are key to plant defense coordination, preserving and enhancing these networks could improve ecosystem resilience. Forest restoration and regenerative agriculture might benefit from strategies that boost mycorrhizal health.

Reduced Reliance on Pesticides

In agricultural settings, encouraging symbiotic fungi could reduce the need for chemical treatments. Crops like coffee, cacao, or potatoes—which naturally associate with fungi—might respond better to stress if embedded in strong fungal networks.

Smarter Experimental Designs

The authors call for experimental validation of their models, suggesting:

1. Genetically modifying plants to block signal emission and test responses
2. Monitoring fungal physiology to track stress detection
3. Testing diverse species and environmental settings for broader insights

“Distinguishing cues from active signals and fungal monitoring is essential for advancing our understanding,” the study concludes.

The Bigger Picture: Cooperation or Self-Interest?

This research upends the popular notion of plant altruism, replacing it with a more nuanced view of evolutionary strategy and ecological complexity.

Even dishonest signaling—where a plant pretends to be under attack to trigger neighbor defenses and gain a competitive edge—may evolve under certain conditions.

The idea that plants might lie, and that fungi may enforce honesty or coordination, adds new depth to how we view underground ecosystems.

Final Thoughts: A Silent Intelligence Below Ground

Fungi, long seen as mere conduits or neutral players, emerge here as active agents shaping the behavior of entire plant communities. Their ability to monitor, relay, and perhaps even regulate defense responses makes them critical to understanding ecological stability.

This study doesn’t just add to our scientific knowledge—it reshapes the narrative of how life communicates, cooperates, and survives.

As climate change and agricultural pressure intensify, understanding the hidden intelligence beneath our feet could help us build more resilient ecosystems—both wild and cultivated.

Topics of interest

Biodiversity