Unexpectedly Deep Plant Roots Raise New Questions About Carbon Storage in Soils: Study

Trees and plants develop vast root networks that extend into the earth to draw water and nutrients from the soil. But how deep do they go?

Until now, scientists thought these roots declined as they moved deeper underground. But new research has found that many plants develop another deeper root layer — often over three feet beneath the soil — in order to access additional nourishment, a press release from New York University (NYU) said.

This could have implications for carbon storage at a time when carbon dioxide levels are at an 800,000-year high, according to the World Meteorological Organization’s most recent State of the Global Climate report.

“An improved understanding of root vertical distribution is crucial for assessing plant-soil-atmosphere interactions and their influence on the land carbon sink,” the authors of the study wrote. “Our analyses suggest that deep soil nutrients tend to be underexploited, while root bimodality offers plants a mechanism to tap into deep soil resources.”

The research revealed plant rooting patterns that had previously gone unrecognized, revising scientific understanding of ecosystems’ response to changing environmental conditions. It also suggested that plants may be transporting and storing carbon deeper than had been believed.

“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,” said lead author of the findings Mingzhen Lu, an assistant professor in New York University’s Department of Environmental Studies, in the press release. “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 researchers used National Ecological Observatory Network (NEON) data to examine the depth of roots. The NEON database has samples collected from soil that is 6.5 feet deep. The unprecedented depth allowed the research team to detect root patterns that spanned diverse ecosystem types and climate zones, from Puerto Rican rainforests to the Alaskan tundra.

Their work considered three main questions that address the resource acquisition strategies of plants, as well as their resilience to environmental change: How does root abundance vary with depth? What factors impact root distribution with depth? Are the nutrients found in deeper soils over-, under- or equally exploited by fine roots in comparison with surface soils?

The team discovered that nearly one-fifth of ecosystems studied had roots that peaked two times across the depth of the soil — a phenomenon known as “bimodality.” These plants developed an additional deeper root layer, often over three feet deep where nutrient-rich soil layers were found.

The findings suggested that plants grew in ways that allowed them 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,” Lu said. “Our limited belowground vision means that we cannot estimate the full ability of plants to store carbon deep in the soil.”

The study, “A continental scale analysis reveals widespread root bimodality,” was published in the journal Nature Communications.

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