Quantifying the footprint of a dominant organism: Impacts of leaf cutter ants on biogeochemical cycling in tropical forests
There is considerable debate in the scientific community about the role of tropical ecosystems in the global carbon budget, partially the result of our incomplete understanding of the C cycle in tropical ecosystems. Matters become more complex when we consider the role of soils in mediating C dynamics – soils are considerably less well-studied in tropical ecosystems and the roles soil invertebrates play in C dynamics are rarely considered. Despite their ecological prominence, we currently know little about the overall contribution of leaf cutting ants to the C cycle. In the summer of 2014, I started a 3 year NSF funded collaborative project to better understand the controls on biogeochemical cycling inside leaf cutter ant nests and to scale those effects up from nests to forest ecosystems. Collaborating with scientists from University of California, Florida International University, University of Auckland, and the University of Costa Rica, we are assessing the role leaf cutter ants play in above and belowground C and biogeochemical dynamics in tropical forests. Our field site is located at La Selva Biological Research Station, in the lowland tropical wet forest in Costa Rica. Our preliminary data, collected largely with help from undergraduate students, shows that CO2 emissions from nests are at least 2x greater than from surrounding forest soils. Nests also appear to be enriched in N and P, confirming that they these nests are hotspots of biogeochemical cycling and CO2 emissions.
Visit the project website at www.attabiogeochemistry.com
In 2015, we organized a "Leaf Cutter Ants and Ecosystem Processes" workshop for undergraduate students interested in ecosystem ecology, tropical biology, leaf cutter ants, biogeochemistry, microbial ecology, and related disciplines at La Selva Biological Research Station, Costa Rica.
The workshop was divided into 3 modules: Part I reviewed the field of microbial ecology through the application of field and laboratory methods. Part II focused on the technical aspects of measuring mycorrhizae and fungal methods. Part III reviewed the techniques to measure soil carbon fluxes and pools. Together, this workshop brought together focused seminars and hands-on activities in the lab and field to answer ecological questions. Students had a chance to develop small independent projects and conduct field work at La Selva Biological Research Station.
THE RESEARCH GROUP
Project Set-Up August 2014, La Selva, Costa Rica
In August 2014, the entire research group met in La Selva to finish plot selection and install the long-term sensor network. In two weeks of intensive field work, we accomplished a lot. We:
(1) selected focal Atta cephalotes nests that will be measured for the duration of the project
(2) installed lysimeters that will collect soil water from 3 soil depths (20cm, 60cm, and 100cm deep) and give us information about carbon losses in dissolved organic and inorganic forms across time
(3) installed gas wells that will allow us to collect soil CO2 from 3 soil depths (20cm, 60cm, and 100cm deep) and tell us not only about soil CO2 concentrations but allow us to measure stable C isotopes
(4) installed soil moisture and temperature probes across a depth profile
(5) extracted soils to quantify fungal infection, collected soil invertebrates associated with Atta cephalotes nests, and exported soils to quantify microbial communities and soil enzyme activity
(6) selected our "super" site, where we will embed an extensive sensor network providing real-time continuous measurements of CO2 diffusion and efflux (embedded soil profile soil CO2 sensors), root and hyphal dynamics (mini-rhizontrons), soil moisture and temperature dynamics, and small cameras that will track ant activity
Taking advantage of the opportunity to brainstorm on the ground, we planned our research campaigns for the next year. Most importantly, we mapped out the long-term vision for how all the discrete data pieces fit together into the modeling framework to quantify the influence of leaf cutters at an ecosystem scale. All in all, this trip was a resounding success and we are leaving La Selva energized and excited about the research ahead!
This project is funded by the National Science Foundation DEB Ecosystems, with additional site support from the Organization for Tropical Studies.