Fungi and the Early Evolution of Terrestrial Ecosystems
When we think of the forces that shaped life on land, plants usually take center stage. But new research published in Nature Ecology & Evolution (Mills et al., 2025) emphasizes that fungi played an equally critical, and often overlooked, role in Earth’s transition from a barren rocky surface to thriving ecosystems.
Fungi Before Forests
The study highlights that fungi colonized land long before vascular plants appeared. Fossil and molecular evidence suggests fungal lineages extend back at least 1 billion years, predating land plants by hundreds of millions of years. These early fungi included both chytrid-like aquatic forms and more advanced Glomeromycotina, which are still known today for forming mycorrhizal partnerships with plants.
This early arrival meant that fungi were already occupying terrestrial niches, weathering rock, cycling nutrients, and establishing soil-like substrates before plants began their terrestrial radiation.
Symbiosis: The Engine of Evolution
One of the paper’s central arguments is that the symbiotic relationship between fungi and early plants was not incidental, but essential for terrestrial colonization.
Arbuscular mycorrhizal fungi (AMF) enabled early bryophyte-like plants to access phosphorus, nitrogen, and water in poor soils.
In return, plants supplied carbon in the form of photosynthates, cementing a metabolic feedback loop that accelerated terrestrial expansion.
Katie J. Field, a co-author and long-time researcher on plant–fungal symbioses, notes that “without fungi, early land plants would likely have been severely constrained in their growth and ecological spread.”
Ecosystem Engineering
Beyond symbiosis, fungi also acted as ecosystem engineers in their own right:
Rock weathering: Fungal hyphae infiltrated mineral substrates, excreting acids that released nutrients.
Carbon cycling: Saprotrophic fungi decomposed organic matter, regulating early carbon fluxes.
Soil structure: Networks of fungal filaments bound sediments and organic detritus, laying the groundwork for stable terrestrial soils.
These processes not only created habitable niches for plants, but also contributed to long-term climate regulation through enhanced silicate weathering and carbon sequestration.
Fungal Innovations and Diversification
The paper details several major fungal innovations during the Paleozoic:
The evolution of complex fruiting bodies in Ascomycota and Basidiomycota.
Expansion of lichens, symbioses between fungi and algae/cyanobacteria that colonized extreme environments.
The diversification of saprotrophs and pathogens, which reshaped ecological networks and biogeochemical cycles.
Together, these evolutionary steps established fungi not as passive partners, but as active agents shaping terrestrial biodiversity.
Implications for Today
Understanding fungi’s deep evolutionary role is more than historical curiosity. The same principles still apply today:
Modern agriculture relies on harnessing mycorrhizal fungi for nutrient efficiency.
Forest ecosystems depend on fungal symbioses for stability and resilience.
Fungi remain key regulators of the carbon cycle — both as decomposers and as mutualists.
Benjamin J.W. Mills and colleagues argue that by overlooking fungi in Earth system models, we underestimate their impact on global biogeochemistry and climate dynamics.
Conclusion
The research of Mills, Field, Hawksworth, and collaborators reframes fungi as foundational architects of life on land. Long before towering forests, fungal networks were laying the groundwork for terrestrial ecosystems — chemically, biologically, and ecologically.
As this paper demonstrates, to understand the origins of life on land, we must tell the story not only of plants, but of the fungi that enabled and sustained them.
References (as cited in the blog)
Mills, B.J.W., Field, K.J., Hawksworth, D.L., et al. (2025). Fungi and the early evolution of terrestrial ecosystems. Nature Ecology & Evolution.
Field, K.J. (2020). Mycorrhizal fungi as drivers of plant evolution and ecology. New Phytologist.
Hawksworth, D.L. (2001). The magnitude of fungal diversity: the 1.5 million species estimate revisited. Mycological Research.
