global biomass – A new Science paper estimates how much arbuscular mycorrhizal fungi exist on Earth, using measurements from a custom robot and data pooled from more than 300 studies—finding the fungal network is massive in length, but surprisingly smaller than many researcher
The first surprise doesn’t come from the scale—it comes from the number.
Arbuscular mycorrhizal (AM) fungi. the soil-dwelling organisms that trade nutrients with plants. are believed to be behind symbiotic relationships spanning roughly 70 percent of plant species on Earth. They also move carbon: AM fungi haul roughly four billion metric tons of carbon from plants into the soil each year. Yet for all that, researchers have been missing something fundamental—how much fungal life is actually out there.
That gap is what a new paper in Science set out to measure. The study pooled data from more than 300 studies to estimate the total global biomass of AM fungi. and ran headlong into a problem that sounds almost trivial until you see how it breaks the math: fungal biomass depends. in part. on the thickness of fungal filaments. If scientists get the average diameter wrong by even a little, the final estimate can swing dramatically.
To explain how hard it is to estimate something that’s uneven and invisible, co-author Justin D. Stewart, a data scientist at the Society for the Protection of Underground Networks (SPUN), uses a simple image. Imagine lying beneath a tree and trying to determine the average width of all its branches—some long and incredibly thin. others short and thick.
The team didn’t rely on guesswork. They built a custom robot named Prince to capture more than 300,000 measurements of growing fungal networks. Inside the lab, other robotic residents also help with the work—Donna Summer and Aretha Franklin.
Those measurements were combined with mathematical modeling and published data from around the world. With the help of a data visualizer, Moritz Stefaner, the researchers also created an interactive mycorrhizal infrastructure map covering Earth’s landmasses down to each square kilometer.
Stefaner said he was pulled in by the dataset’s aesthetic qualities, and by what it makes possible: “We’re surrounded by numbers and data,” he said. “Everybody wants to make sense of it. Everybody wants to see the big picture.”
So what did they find?
The answer is both larger and smaller than many expectations. By biomass, the world’s AM fungi weigh roughly five times as much as all humans combined. That’s undeniably huge, but it’s not as enormous as many researchers anticipated.
Kyra Skye Gibson. a postdoctoral researcher at Northern Arizona University who was not involved in the study. described the reaction plainly: “I was kind of surprised that the numbers weren’t higher.” Stewart says his team felt the same jolt. too. “When we first calculated how heavy these fungi were. ” he said. “I think we spent two or three weeks recalculating it to make sure we weren’t missing zeros.”.
But mass may not be the best way to picture what’s happening underground. Measured by length, the scale becomes harder to take in. The world’s topsoil contains an estimated 110 quadrillion kilometers of AM fungi laid end to end—enough. the study says. to stretch from Earth to our neighboring star Proxima Centauri and back. or to reach 11.9 light-years to Tau Ceti. the setting of Andy Weir’s sci-fi hit Project Hail Mary.
The staggering numbers are one thing. The bigger challenge is what they still can’t pin down.
Stewart doesn’t want the maps to be treated like finished facts. “We’re treating these maps as living documents. not static images. ” he said. stressing the work still required by nearly 200 researchers working with SPUN to fill in remaining gaps. To make those gaps visible. the team created supplemental “maps of ignorance” designed to highlight where their estimates are most uncertain.
Stewart said he’s comfortable living with uncertainty as long as it’s quantified—“as long as we quantify what type of uncertainty it is and how large it is.” For him. those maps are more than a warning label. “These maps of ignorance are also treasure maps of where we need to go sample data in the future.”.
In the end, the study delivers a rare kind of scientific momentum: a first global estimate grounded in hard measurements, paired with a clear roadmap for what must be tested next.
arbuscular mycorrhizal fungi AM fungi soil fungi fungal biomass mycorrhizal networks underground networks Science paper Prince robot SPUN global fungal estimates carbon cycling Moritz Stefaner maps of ignorance