A new global study has found that plants’ root system includes a second “secret” set of deep roots that reach farther underground than once believed, opening new possibilities for carbon storage and plant survival in harsh soil conditions.
Researchers analyzed soil samples from 44 sites worldwide, ranging from the icy Alaskan tundra to the lush rainforests of Puerto Rico. The samples were collected from more than 6 feet (1.8 meters) beneath the surface, far deeper than most studies usually reach.
The study, published June 17 in Nature Communications, found that around 20% of the sites had what scientists call “bimodality” rooting systems. That means plants had two major zones of root growth, one near the surface and another deeper underground.
“This was surprising,” said Mingzhen Lu, the study’s lead author and an ecologist at New York University. “For a long time, scientists thought roots mostly fade out as you go deeper. But we’re seeing something different; many plants are growing deep roots if conditions call for it.”
Deep roots offer backup when topsoil fails
These deep roots often tap into lower layers of soil, which are rich in nutrients such as nitrogen. These roots can provide plants with an additional source of support when the upper soil dries out or lacks nutrients. While most plants gather water and nutrients from the surface, aided by rain and fallen leaves, this secondary root system provides some plants a backup plan when surface supply proves insufficient.
Lu stated that not all plants develop this secondary system; it appears to occur when there is a specific reason. “It is more of a choice,” he said. “Given enough motivation… plants will explore deeper and make use of these deep resources.”
The study raises new questions about what scientists know about subterranean processes. Many past studies only sample the first few inches of soil. Lu said that the approach misses key information. “Sampling 10 centimeters [4 inches] deep, or 30 centimeters [12 inches], simply won’t cut it,” Lu said. “We just miss too much of what’s actually going on in the soil.”
Study challenges long-held assumptions
Alain Pierret, a soil scientist with the French National Research Institute for Sustainable Development who was not involved in the study, called the findings important. He said earlier research hinted at deep roots but lacked the wide sampling used in this study.
Pierret added that these deep root systems may be more complex than the current data shows. They’re likely not just bimodal but multi-modal, he said, with roots possibly growing even farther down.
The findings also have climate implications. Soil holds more carbon than the atmosphere, and deep roots can move carbon farther underground. Lu said this could mean plants are already doing more to slow climate change than scientists realized.
“The good news is plants may already be naturally mitigating climate change more actively than we’ve realized,” Lu said. “We just need to dig deeper to fully understand their potential.”