Bridging the surface and subterranean

What happens when you bring a plant physiologist into a cave? What about bringing a cave biologist above ground and into the forest? Chances are that both will feel outside of their comfort zone but there is a lot that we can learn from changing perspectives. And this is exactly what my research does.

During my time in graduate school, I have been investigating the relationships between the above and below ground by studying tree roots growing into caves in Quintana Roo, Mexico. I am specifically interested in identifying which trees are capable of rooting deeply, determining if they are accessing deep sources of water and nutrients, and if so, how does this access impacts surface process, mainly productivity and forest composition.

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Rory O’Keefe looks at a large root mass in a cave in Quintana Roo. Photo by Rory O’Keefe.

Over the course of my studies, the division between tropical forest, cave, and karst aquifer research has been apparent. However, in Quintana Roo, the surface and subterranean are directly linked via the roots, making the two difficult to separate. Once you venture inside of the caves, it is common to see tree roots growing through the ceilings and walls. These can range from fine roots to substantial networks of large coarse roots that can look like speleothems (cave formations) at first glance.

Deep roots can potentially access water within the cave from pools or directly from the karst aquifer. This is seemingly more reliable than shallow water in soil or bedrock. If select species utilize this water, it may contribute to differences in plant performance, species dominance, and competition that are observed above ground. Root growth, however, is limited by space within the bedrock. This space can be expanded by dissolution of the limestone and physical pressure on the rocks from root enlargement. Yet, this takes time.

If a root makes its way into the cave, it is can be a substantial source of organic matter within an otherwise nutrient-deficient environment. Roots have been noted as being important food and shelter for subterranean fauna in caves in Western Australia and Hawaiian lava tubes. In Quintana Roo, cave-adapted (blind and pigmentless) critters like isopods are frequently observed around fine roots in pools. I have seen animals from the surface, like snails and ants, on the roots as well.

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A cave-adapted isopod is nestled among roots in a pool. Photo by Rachel Adams.

An interesting observation I have made at my study sites is the presence of moonmilk at the root-rock interface within the caves. Moonmilk is a type of biokarst that is believed to be the result of calcite precipitating bacteria. The root is probably a crucial source of carbon for the bacteria, allowing for significant moonmilk deposits. To my knowledge, there have not been studies conducted on the interactions between the roots, moonmilk, and bedrock within the caves here.

My research is rather foundational because little work has directly addressed the roots in the caves, even after they have been seen and photographed by an innumerable number of people. Identifying the roots to species was a critical first step and I can finally tell tourists, cavers, and land owners, which species are present in the caves. But believe me, I feel like I have so many more questions than answers right now!

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Observing the forest from below. Photo by Rachel Adams.

While connections between the surface and subterranean may be inherent, there is much to learn about linkages between the above and below ground to better understand ecosystems holistically. Whole system studies are important because they allow us to understand how one aspect affects another. Biodiversity can play a key role in these processes between the plant, microbial, and subterranean community that would otherwise be overlooked if research is divided between the above and below ground components. Collaboration across fields, like between plant physiologists and cave biologists, can facilitate such insights.

I am fascinated by the interplay between above and below ground processes and various biotic and abiotic environmental factors. As I begin the next step in my career, I want to continue interdisciplinary work that brings together different fields to focus on the intersections between plants, soils, and geology, especially in karst systems. I hope to address questions that have broad impacts and implications for conservation and management practices.

 


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