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Unexpectedly deep roots in plants unearth new questions about soil carbon storage

Plants and trees extend their roots into the earth in order to draw nutrients and water from the soil—however, these roots are thought to decline as they move deeper underground. But a new study by a multi-institutional team of scientists shows that many plants develop a second, deeper layer of roots—often more than three feet underground—to access additional nourishment.

Published in the journal Nature Communications, the reveals previously unrecognized rooting patterns, altering our understanding of how ecosystems respond to changing environmental conditions.

More importantly, the study suggests that plants might transport and store fixed carbon deeper than currently thought—welcome news at a time when CO₂ levels are at an 800,000-year high, according to the World Meteorological Organization's "" issued in March 2025.

"Understanding where plants grow roots is vital, as deeper roots could mean safer and longer-term carbon storage. Harsher conditions at depth may prevent detritus-feeding microbes from releasing carbon back to the atmosphere," says Mingzhen Lu, an assistant professor at New York University's Department of Environmental Studies and the paper's lead author.

"Our current ecological observations and models typically stop at shallow depths; by not looking deep enough, we may have overlooked a natural carbon storage mechanism deep underground."

The research team used data from the National Ecological Observatory Network (NEON) to examine rooting depth. The NEON database includes samples collected from soil 6.5 feet below the surface, far deeper than the one-foot depth of traditional ecological studies.

This unprecedented depth allowed researchers to detect additional root patterns, spanning diverse climate zones and ecosystem types from the Alaskan tundra to Puerto Rico's rainforests.

The scientists' work focused on three questions—all with the aim of better understanding plants' resource acquisition strategies and their resilience in response to environmental change:

• How does the abundance of roots change with depth?
• What are the factors that impact the distribution of roots with depth?
• Are nutrients in deeper soils equally, under-, or over-exploited by fine roots compared with surface soil?

The researchers found that nearly 20% of the studied ecosystems had roots that peaked twice across depth—a phenomenon called "bimodality."

In these cases, plants developed a second, deeper layer of roots, often more than three feet underground and aligning with nutrient-rich soil layers. This suggests that plants grew—in previously unknown ways—to exploit additional sustenance.

"The current understanding of roots is literally too shallow. Aboveground, we have eagle vision—thanks to satellites and remote sensing. But belowground, we have mole vision," observes Lu, former Omidyar Fellow who conducted part of this research at the Sante Fe Institute and as a postdoctoral affiliate at Stanford University.

"Our limited belowground vision means that we cannot estimate the full ability of plants to store carbon deep in the soil."

"Deep plant roots may cause increased soil carbon storage in one condition or lead to losses in other conditions due to a stimulation of soil microbes," suggests co-author Avni Malhotra, the lead author of a that investigated the connection between root distribution and soil carbon stock.

"This discovery opens a new avenue of inquiry into how bimodal rooting patterns impact the dynamics of nutrient flow, water cycling, and the long-term capacity of soils to store carbon."

"Scientists and policymakers need to look deeper beneath Earth's surface as these overlooked deep soil layers may hold critical keys for understanding and managing ecosystems in a rapidly changing climate," concludes Lu.

"The good news is plants may already be naturally mitigating climate change more actively than we've realized—we just need to dig deeper to fully understand their potential."

The study also included researchers from Boston College, Columbia University, Dartmouth College, the Morton Arboretum, the National Ecological Observatory Network-Battelle, Pacific Northwest National Laboratory, and Stanford University.