Decomposition is the process through which tiny organisms, fungi, and bacteria in the soil (known as decomposers) take organic matter (i.e., any matter that originates from living things) and turn it into nutrients and minerals. Through decomposition, organic matter is restored to the soil and provides plants and small organisms with the food they need to grow.

The effectiveness of soil decomposers, however, depends on various environmental factors, such as humidity, acidity, temperature, and the nutrients availability. For example, decomposition is slower in cold climates and quicker in hot climates. Acidic, dry, and nutrient-poor soils are less suitable for decomposition as well.

When decomposers become more active, they release more carbon dioxide (CO2), a greenhouse gas, into the atmosphere. Just like humans who breathe out CO2, microorganisms produce CO2 when they metabolize and break down organic matter. As CO2 is partly responsible for climate change, it is essential to monitor it by observing the reactions of the soil and its organisms.

The use of tea bags for science had its beginnings in the Netherlands, when a couple of students took a soil ecology course in 2010. That is when they had the idea for a standardized tea-bag-based methodology. After three more years of fine-tuning, it was in 2013 when they officially published their method. Tea was chosen, out of all the organic matter they tested as potential experimental raw material, because it was cheaper and easy to get. It also comes pre-bagged and ready for use, with its plant materials duly inspected and measured out. The protocol the Dutch researchers developed involves burying two kinds of tea (rooibos and green) in the soil, then measuring the change in mass after 3 months. In 2015, the Tea Bag Index got support from the Swedish government and Vetenskapsrådet (Swedish Research Council), followed by global recognition. Besides their local experiments, a Scandinavian team expanded into international citizen science by giving everyone the opportunity to apply the protocol and send in their results to the original team using an online portal. The method has spread around the world and is now being used by many other research projects worldwide.

To be specific, the protocol calls for measuring the loss in mass: 1) of a bag of green tea, which decomposes rapidly, and 2) of a bag of rooibos tea, considered more resistant to decomposition. The results are used to work out the decomposition rate mathematically and identify stabilizing factors, such as temperature and humidity, that control the activity of decomposers.

The MELCCFP has been using the tea bag protocol for its Biodiversity Monitoring Network to track the effects of climate change on decomposition rates in Quebec soils since 2016. Since then, more than 400 tea bags have been buried in Quebec, dug up 90 days later, and weighed.

Since the climate affects the speed of decomposition, scientists can draw conclusions from the variation in the loss of mass they record at different burial sites. By regularly going back to the same site, they can find out if decomposition is speeding up as the climate gets hotter, or how environmental changes are affecting the state of agricultural and forest soils.

Some of you might already be thinking you’d like to join this group effort and stash a few tea bags in your backyard but keep in mind that it’s not that easy. The protocol is based on a specific brand and blend of tea only sold in European grocery stores. This means that to stock up, the MELCCFP must import crates of tea bags, all the way from Germany. It’s always kind of a wacky order to place!