36000 buried tea bags aid science and bring to light the importance of soil

36000 buried tea bags aid science and bring to light the importance of soil

Hobby project went viral by accident

By burying 36,000 tea bags and retrieving them three months later, researchers and citizen scientists worldwide gathered data on the decomposition of plant material in soil. This allowed a team of researchers to develop global maps that are useful for climate models, and to take a first step towards a deeper understanding of subterranean decomposition processes. Utrecht University researcher Joost Keuskamp: "This would never have been possible without the extensive collaboration between a great many people."

Decomposition processes in the soil influence the levels of CO₂ in the atmosphere and the carbon content in the soil. Plants capture CO₂ through photosynthesis. When plant material dies, it is decomposed by fungi and bacteria, releasing much of the stored CO₂ back into the air. However, not all of the CO₂ returns to the atmosphere; some of the plant material is transformed into humus, which remains in the soil for an extended period.

How these processes vary across different locations on Earth and climates is not entirely clear. Yet this knowledge is crucial for predicting the implications of climate change on soil carbon balance and the release of CO₂ from decomposing plant material.

Joost Keuskamp

Tea bags

That is one of the reasons Keuskamp wanted to gather extensive data on soil decomposition processes at many different locations across the globe. But how exactly does one do this?

Keuskamp: "We came up with the idea of asking people to take measurements using tea bags produced by a major food manufacturer. This manufacturer excels in standardization: the tea is a blend, and the content of each bag is pretty much the same. Moreover, the tea is available in many countries and packaged in plastic pouches with the appropriate mesh size, allowing fungi and bacteria to enter while the plant material cannot get out."

Want to participate?

Would you like to join the project by burying tea bags? Visit the new Tea Bag Index website for instructions.

Green tea and rooibos

Participating was simple: individuals only had to purchase green tea and rooibos from a specific brand and bury one bag of each type in the ground. After three months, they retrieved the bags, allowed them to dry, and weighed the remaining material.

Tea bags were buried in a wide range of locations.

Keuskamp: "Green tea consists of leaves that decompose easily, whereas rooibos consists of twigs that break down more slowly. After three months, all easily degradable material from the green tea had typically decomposed, whereas the decomposition process was still ongoing for rooibos. Therefore, green tea helps determine the amount of remaining material at a specific location, while rooibos provides insights into the rate of decomposition at that spot."

Viral

Initially, the researchers intended to only ask other scientists to collect data. However, when the project launched, it gained global media attention, and many non-scientists expressed interest. Keuskamp: "It started out as a hobby project, but went viral. We had already invested significant effort in making the project accessible and well-communicated, as we also wanted to use the experiments as an educational project for schools. I even discussed the project with drunk people in the pub, to see if I could keep their interest for long enough."

Insights

The results from the 36000 tea bags enabled the researchers to create global maps of subterranean decomposition and to explore relationships between decomposition processes and environmental factors.

They uncovered some surprising and previously unknown patterns. For instance, the researchers observed relatively fast decomposition in cold regions, while a lot of material was still there in the end. They also found that agriculture influenced the rate of decomposition, but not the amount of remaining material. This shows that the rate of decomposition and the final amount of remaining material are not always linked. These new insights could lead to climate models capable of more accurately predicting CO₂ production from soil decomposition processes.

Underpants and tea bags, those are the things we got to work with.

Impact

Recently, an article about the project was published in the scientific journal Ecology Letters. First author Judith Sarneel of Umeå University: "Engaging so many researchers and citizen scientists in understanding soil processes is a great win, benefiting both our scientific knowledge as well as promoting sustainable land use and awareness of it."

Keuskamp thinks that the non-scientific impact of the project may be even more substantial than its scientific impact. The project brought to light the typically invisible decomposition processes in the soil, which also play a significant role in biodiversity, to citizens, schoolchildren, and students.

Keuskamp views it as the task of universities to conduct outward-focused research. In this context, he highlights the benefit of using garden-variety items for measurements. "Many things are the same everywhere, allowing people from all over the world to participate." He references a project of Canadian origin where participants are asked to bury underpants in their gardens to gain insight into the soil life there: "Underpants and tea bags, those are the things we got to work with."

Publication

Reading tea leaves worldwide: Decoupled drivers of initial litter decomposition mass-loss rate and stabilization

Judith M. Sarneel, Mariet M. Hefting, Taru Sandén, Johan van den Hoogen, Devin Routh, Bhupendra S. Adhikari, Juha M. Alatalo, Alla Aleksanyan, Inge H. J. Althuizen, Mohammed H. S. A. Alsafran, Jeff W. Atkins, Laurent Augusto, Mika Aurela, Aleksej V. Azarov, Isabel C. Barrio, Claus Beier, María D. Bejarano, Sue E. Benham, Björn Berg, Nadezhda V. Bezler, Katrín Björnsdóttir, Martin A. Bolinder, Michele Carbognani, Roberto Cazzolla Gatti, Stefano Chelli, Maxim V. Chistotin, Casper T. Christiansen, Pascal Courtois, Thomas W. Crowther, Michele S. Dechoum, Ika Djukic, Sarah Duddigan, Louise M. Egerton-Warburton, Nicolas Fanin, Maria Fantappiè, Silvano Fares, Geraldo W. Fernandes, Nina V. Filippova, Andreas Fliessbach, David Fuentes, Roberto Godoy, Thomas Grünwald, Gema Guzmán, Joseph E. Hawes, Yue He, Jean-Marc Hero, Laura L. Hess, Katja Hogendoorn, Toke T. Høye, Wilma W. P. Jans, Ingibjörg S. Jónsdóttir, Sabina Keller, Sebastian Kepfer-Rojas, Natalya N. Kuz'menko, Klaus S. Larsen, Hjalmar Laudon, Jonas J. Lembrechts, Junhui Li, Jean-Marc Limousin, Sergey M. Lukin, Renato Marques, César Marín, Marshall D. McDaniel, Qi Meek, Genrietta E. Merzlaya, Anders Michelsen, Leonardo Montagnani, Peter Mueller, Rajasekaran Murugan, Isla H. Myers-Smith, Stefanie Nolte, Raúl Ochoa-Hueso, Bernard N. Okafor, Vladimir V. Okorkov, Vladimir G. Onipchenko, María C. Orozco, Tina Parkhurst, Carlos A. Peres, Matteo Petit Bon, Alessandro Petraglia, Martin Pingel, Corinna Rebmann, Brett R. Scheffers, Inger Schmidt, Mary C. Scholes, Efrat Sheffer, Lyudmila K. Shevtsova, Stuart W. Smith, Adriano Sofo, Pablo R. Stevenson, Barbora Strouhalová, Anders Sundsdal, Rafael B. Sühs, Gebretsadik Tamene, Haydn J. D. Thomas, Duygu Tolunay, Marcello Tomaselli, Simon Tresch, Dominique L. Tucker, Michael D. Ulyshen, Alejandro Valdecantos, Vigdis Vandvik, Elena I. Vanguelova, Kris Verheyen, Xuhui Wang, Laura Yahdjian, Xaris S. Yumashev, Joost A. Keuskamp

Ecology Letters, 7 May 2024. DOI: https://doi.org/10.1111/ele.14415