Identifying the biodiversity of the Mayan underworld

In the caves of Quintana Roo, there are not only stalactites hanging from the ceiling. There are tree roots too, but the roots of which trees?

Tourists in Quintana Roo, Mexico often visit the caves of the region. The caves entice people in with shimmering blue water and breathtaking geological features. But in the caves are something else, something that brings life to a habitat that would otherwise be still and silent. In the caves of Quintana Roo, you can find plants. While on the surface, you see the top half of the plant, it’s in the caves that you can see the hidden part of the plants with their twined and complicated root systems. But the roots of which plants? Rachel Adams and colleagues examined the caves to find out. “[I]nterest and research about forest and caves are often separated,” write Adams and colleagues in their paper. “Forest ecologists focus on the aboveground component, cavers focus on the belowground. However, these two are difficult to separate ecologically considering that the roots directly connect the surface and the subterranean. In our view, there is an opportunity to enhance what tourists get out of visiting these beautiful cave systems by better understanding how the aboveground forest is intimately linked with the cave environment and remembering that the roots are integral to symbolic Maya world tree.”

A cave in Quintana Roo. Image: Canva.

To examine the roots, the team visited five caves in the state of Quintana Roo, looking for differences in the shape and structure of the roots. They categorized the roots, and then tested the idea that distinct categories belonged to different species by taking samples of the roots and DNA barcoding them.

Some of their results, such as Ficus roots, were expected. Ficus trees often grow around cenotes, openings to the cave system. But some plants were unusual. “A notable and surprising observation was the roots of a palm (Sabal yapa C. Wright ex Becc.), a seemingly shallow‐rooted species, emerging from stalactites up to 5 meters below the surface,” write the authors.

Learning about the diversity of the plants in the aquifers could help us understand the ecosystems they underpin, said Adams and colleagues in their paper. “In submerged cave systems, bundles of fine roots are suspended in the water column and flow with the current. Where there are roots, there is also heterotrophic life. Cave environments are considered to be nutrient‐deficient, subject to organic matter that falls or washes in. Therefore, tree roots provide an excellent source of food and shelter for subterranean animals, trogloxenes (cave visitors) and troglobites (cave dwellers) alike.”

“Understanding the holistic interactions between the surface and subterranean will better inform us about species‐specific characteristics, biogeochemical processes occurring in the rhizosphere, and groundwater reliance in understudied tropical forests. This should contribute to protection and better management of the resources and ecosystem services that tropical forests and caves provide, especially in the face of expanding urbanization in Quintana Roo.”