How Do Fungi Keep the Planet Healthy?

Mycorrhizal fungi form intimate, long-standing partnerships with over 80% of Earth’s plant species, a relationship that evolved around 450 million years ago. These fungi, whose name comes from the Greek words for fungus (myco) and root (rhizal), act as an extension of plant roots by supplying essential minerals like phosphorus and nitrogen, which they extract from rocks and soil. In return, plants provide fungi with sugars and fats produced through photosynthesis. This exchange is so fundamental that fungi essentially served as plant root systems for tens of millions of years before roots evolved as a distinct plant feature. The partnership is one of the oldest and most widespread biological collaborations, underpinning terrestrial ecosystems today.

Mycorrhizal fungi create vast, interconnected networks of thread-like structures called hyphae, which are thinner than human hairs. Some networks, like those formed by arbuscular mycorrhizal fungi, operate as single, continuous cells without internal walls, resembling the largest cells on Earth. These networks function as a two-way supply chain: plants send carbon-based nutrients down to the fungi, while fungi transport minerals and water upward to the plants. The flow of nutrients occurs simultaneously in opposite directions within the same network, a process scientists compare to a river flowing north and south at once. Researchers use advanced tools like fluorescent labeling and imaging robots to study these networks, tracking up to half a million nodes to understand how fungi navigate and make decisions underground.

Mycorrhizal fungi play a critical role in regulating Earth’s climate by sequestering approximately 13 billion tons of atmospheric carbon dioxide annually. This amount is roughly equivalent to one-third of global fossil-fuel emissions. Plants absorb carbon from the atmosphere and allocate a significant portion of it to fungal networks, where it is stored deep in the soil. The fungi help lock carbon underground by producing stable, slow-to-decompose compounds that bind soil particles together. Without these networks, soil erosion would increase, and carbon stored in the ground could be released back into the atmosphere. This process makes fungi an unsung hero in the fight against climate change.

Despite lacking a brain or nervous system, mycorrhizal fungi exhibit strategic behavior in their partnerships with plants. Research by evolutionary biologist Toby Kiers and her team at Vrije Universiteit Amsterdam suggests that fungi can discriminate between better and worse trading partners, shifting resources to plants that offer more favorable exchanges. Using principles from economics and game theory, scientists have observed that fungi allocate more nutrients to plants that provide higher-quality carbon sources, such as fats and sugars. This decision-making process is driven by molecular mechanisms, including pressure gradients and lipid transport within the fungal network, allowing fungi to optimize their resource allocation.

Mycorrhizal fungi are indispensable to agriculture and human life. Up to 80% of a plant’s phosphorus intake first passes through fungal networks before reaching the plant, meaning even the phosphorus in human DNA ultimately originates from fungi. These networks enhance soil fertility, improve water retention, and help plants resist diseases and environmental stresses. By supporting plant health, fungi contribute to food security and biodiversity. Additionally, their role in carbon sequestration and soil structure makes them vital for sustainable farming practices. Protecting these underground networks is essential for maintaining healthy ecosystems and mitigating climate change.