雅思阅读 087: The Fungal Internet — Earth's Hidden Underground Network

Adapted from "See the hidden fungal network so big it could stretch to Proxima Centauri and back" by Sam Macdonald, Scientific American, 11 June 2026.

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Reading Passage

If you have never heard of arbuscular mycorrhizal (AM) fungi, you are not alone — unless you happen to be a plant. These underground organisms form symbiotic partnerships with roughly 70 percent of plant species on Earth. Yet although they haul four billion metric tons of carbon from plants into the soil every year, scientists have never known exactly how much of this fungus exists globally — until now.

In a paper published in Science, researchers combined data from more than 300 studies to estimate the total global biomass of AM fungi. The task is harder than it sounds: biomass depends on the thickness of fungal filaments, and even a small error in estimating their average diameter can dramatically change the final number.

To solve the problem, the team used a custom-built robot named Prince, which captured over 300,000 measurements of growing fungal networks. Combined with mathematical models and data from around the world, these measurements allowed the team to produce the first high-resolution global map of AM fungi, covering every square kilometre of Earth's landmasses.

The results are striking. By weight, the world's AM fungi are roughly five times heavier than all humans combined. That is substantial but smaller than many researchers expected. "I was kind of surprised the numbers weren't higher," says Kara Skye Gibson of Northern Arizona University, who was not involved in the study. The team itself spent weeks recalculating to make sure they had not missed any zeros.

Perhaps mass is the wrong measure. In terms of total length, the fungal filaments — called hyphae — are staggering. Laid end to end, the network would stretch to Proxima Centauri, the nearest star beyond the Sun, and back.

AM fungi weave themselves into plant roots. The fungal filaments break down minerals in the soil that plants cannot access directly, while the plants supply the fungi with sugar from photosynthesis. This underground web can connect trees of different species, allowing nutrients and warning signals to pass between them.

The new global map reveals where the fungal networks are thickest: in tropical forests, grasslands and agricultural soils, where warm temperatures and abundant roots support rapid fungal growth. In desert regions, fungal biomass drops sharply.

The findings have immediate relevance for climate change. Because AM fungi transfer huge amounts of carbon into the soil, protecting them could be a valuable tool for carbon capture. Tillage, deforestation and overgrazing destroy fungal networks, releasing stored carbon back into the atmosphere.

"We're surrounded by numbers," says data visualiser Moritz Stefaner, who helped create an interactive map of the fungal world. "Everybody wants to see the big picture." Now, for the first time, they can.

Questions 1–5

Choose the correct letter, A, B, C or D.

1. Approximately what percentage of plant species form partnerships with AM fungi?

   • A. 30 percent
   • B. 50 percent
   • C. 70 percent
   • D. 90 percent

2. How many metric tons of carbon do AM fungi move from plants to soil each year?

   • A. 400 million
   • B. 4 billion
   • C. 40 billion
   • D. 400 billion

3. The robot used by the research team was named

   • A. Donna Summer.
   • B. Aretha Franklin.
   • C. Prince.
   • D. Stewart.

4. By weight, AM fungi are about how many times heavier than all humans?

   • A. Two
   • B. Three
   • C. Five
   • D. Ten

5. Where is fungal biomass thickest?

   • A. In deserts and polar regions
   • B. In tropical forests and grasslands
   • C. In deep ocean sediments
   • D. On mountain peaks

Questions 6–10

Do the following statements agree with the information?

Write:

• TRUE
• FALSE
• NOT GIVEN

6. Fungal filaments are called hyphae.
7. The fungi give sugar to plants.
8. The team was initially sure their calculations were correct.
9. AM fungi can transfer warning signals between different tree species.
10. Tillage and deforestation help fungal networks grow.

Questions 11–13

Complete the summary. Choose ONE WORD ONLY.

The fungi provide plants with minerals from the 11 while plants supply the fungi with 12 from photosynthesis. Protecting fungal networks could help capture 13 from the atmosphere.

Answers

1. C — "roughly 70 percent of plant species on Earth."
2. B — "roughly four billion metric tons of carbon."
3. C — "a custom-built robot named Prince."
4. C — "roughly five times as much as all humans combined."
5. B — "thickest: in tropical forests, grasslands and agricultural soils."
6. TRUE — "the fungal filaments — called hyphae."
7. FALSE — Plants supply sugar; fungi supply minerals.
8. FALSE — They spent weeks recalculating.
9. TRUE — "nutrients and warning signals to pass between them."
10. FALSE — Tillage and deforestation "destroy fungal networks."
11. soil
12. sugar
13. carbon

Key Vocabulary