Tropical tree roots represent an underappreciated carbon pool

October 12, 2017, Smithsonian Tropical Research Institute
The root systems of tropical trees may represent 30 percent of the total tree biomass. Credit: Jefferson Hall

Ask someone to draw a tree and s/he will invariably draw a trunk and branches—leaving the roots out of the picture. In a unique study of tropical tree roots at the Smithsonian Tropical Research Institute published in PLOS ONE, roots accounted for almost 30 percent of the total biomass of young trees. The authors hope that future estimates of carbon storage and water-use by tropical forests will include information on root biomass and architecture.

"Studies like the article published by Baccini et al in the Sept. 28 issue of Science use satellite data to measure aboveground carbon density," said Jefferson Hall, director of the Smithsonian's Panama Canal Watershed (Agua Salud) experiment. "It is fairly common practice to calculate forest either incorporating root mass via a fudge-factor, or leaving it out altogether. What percentage of a tree is underground? How does this change with climate, soil fertility, and over time? The answers to these questions will refine our ability to understand how forests respond to global change."

"During the rainy season in 2009, our team excavated all roots down to 2 millimeters in diameter from six species of tropical ," said Katherine Sinacore, doctoral student at the University of New Hampshire. "We chose six to eight-year old trees from reforestation experiments at Sardinilla and in Soberania National Park in the Panama Canal Watershed, with permission from Panama's Ministry of the Environment." Support for this project was provided by Panama´s Office of National Science and Technology, SENACYT, Mr. Stanley Motta, Mr. Frank Levinson, the Hoch family, the Agua Salud Foundation and the Panama Canal Authority.

"There were huge differences among species," Sinacore said. "We found that trees have very different architectures. For example, some species invest in a large tap root that descends directly below the trunk while other species send large roots out laterally just below the soil surface. These trees sent smaller roots down from the that, when excavated, resembled tentacles of an octopus. The tentacles went just as deep as did the tap roots of other species such that the trees were not trading off structural differences for the ability to seek nutrients and water deep in the soil. In fact, we did not detect a difference between species in the volume of soil reached by roots. We also found roots extending more than 20 meters (60 feet) away from the tree trunk."

The six trees in the experiment, Anacardium excelsum (Espave in Spanish), Cedrela odorata, Dalbergia retusa (Cocobolo), Pachira quinata (Cedro Espino), Tabebuia rosea (Roble) and a (Amarillo), all have high timber value and are commonly used for reforestation in Panama."Perhaps not surprisingly, we found root systems to be every bit as diverse as the crowns of trees, a morphological diversity that is important to understand as it suggests a more thorough exploitation of belowground resources," said Hall. "Interestingly, we also found that two of the forty trees (5 percent) we excavated (a Terminalia Amazonia and a Pachira quinata) were connected with neighboring via grafts of coarse roots. Are these trees sharing resources? Would we have found a higher percentage of grafts if we would have had the ability to look at fine roots? Clearly there is more work to be done."

Explore further: Panama's native tree species excel in infertile tropical soils

More information: Katherine Sinacore et al, Unearthing the hidden world of roots: Root biomass and architecture differ among species within the same guild, PLOS ONE (2017). DOI: 10.1371/journal.pone.0185934

Related Stories

Downed trees not necessarily a lost cause

September 19, 2017

Among the devastation wrought by Hurricane Irma last week, many downed trees and uprooted plants were left in the storm's wake. Those in a rush to get things back to normal have been quick to break out the chainsaws and remove ...

Deep roots in plants driven by soil hydrology

September 18, 2017

Searching for water, some tree roots probe hundreds of feet deep and many trees send roots through cracks in rocks, according to a new study led by a Rutgers University-New Brunswick professor.

Recommended for you

Sahara dust may make you cough, but it's a storm killer

July 20, 2018

The bad news: Dust from the Sahara Desert in Africa—totaling a staggering 2 to 9 trillion pounds worldwide—has been almost a biblical plague on Texas and much of the Southern United States in recent weeks. The good news: ...

Human influence detected in changing seasons

July 20, 2018

For the first time, scientists from Lawrence Livermore National Laboratory (LLNL) and five other organizations have shown that human influences significantly impact the size of the seasonal cycle of temperature in the lowest ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.