Practical questions

What is the method?

In short: You bury two tea bags, wait three months, retrieve and dry them and measure their weight loss. More details can be found under ‘Method’.

What do I need?

You need a scale that can weigh the tea with two or three decimals precisely. Further, the right tea and something to dig a hole. A ruler can be handy to measure the depth of the hole. See also the method section in the menu bar.

Why can I not dig down tea in my garden or in a pot?

Your garden likely contains many plants that are not typical of the plant community and the climate that you are living in. Many gardens are also fertilized and have soils added from other regions. As all these factors affect decomposition, burying tea inside your garden will not give values that are representative of the natural soil around you. As we model large scale gradients, based on average conditions, we have to make sure that the measurements are also taken from locations that represent those average conditions. Gardens usually represent very local conditions. However, if your garden is very natural and representative of undisturbed, natural soil, you can bury the tea inside your garden.

Why do you use plastic teabags?

Because we are interested in the tea inside and plastic does not decompose. Remember that after the experiment you do not throw your tea bags with the organic material, as the tea bags are plastic.

What does air dried mean?

Air dried means dried under ambient conditions to the air, without applying any special drying treatment, e.g. by using an oven. The bags are air dry when they feel and look dry. Tea comes air dry from the package. Also when you have placed them in the sun for a few days, you can consider your tea to be air dried.

Where and when should I bury my tea?

You can bury tea where you think it is interesting. We prefer natural soils over gardens. Ideally, the incubation period should include the growing season as this is usually the period in which soils are most active. We foresee that in the future, when the database grows, it will be possible to include changes in decomposition during the year. In TBI 1.0 and 2.0 we aim to get growing season values.

My tea bag has a hole, can I still submit the data?

No, because tea can be lost from the hole. We can therefore not be 100% sure that the measured weight loss was due to decomposition.

Roots grew into my bag, what should I do?

Remove all roots carefully from the bag. Sometimes it is necessary to open the bag. Do this very carefully so that you do not lose any tea or mix tea with the soil outside on the bag. The best is than to take another container (e.g. a paper cupcake form) and dry the tea in there after picking out the roots. Weigh the tea together with the (now) empty bag, and subtract the weight of the container. This is because the data submission form asks you for the total amount of tea and bag and rope (without the label).

Soil came into my bag, what should I do?

If you are a researcher, you can use the Los On Ignition method to determine the weight of the tea. If you are a citizen scientist, remove the soil as good as you can, and write a note about this in the comments section when you submit your data.

I lost one of the tea bags.

That is a pity, we cannot use the data. We need both tea types for the calculation. Thank you for your effort none the less!

I lost the rope and the label.

You can still submit the data, as long as you know which bag is which type of tea. This can also be detected visually. The green tea usually dries to a solid grain whereas Rooibos is looser and course in structure. Usually the rooibos teabag contains more material compared to the green tea that can be nearly empty. Either weigh the bag that lost its label with the rope of another bag or add 0.03 or 0.029 to the weight, depending on the precision of the scale that you used.

Why should I remove the label before I determine the endweight of the bags?

The label consists of paper and plastic. The paper will also decay during the incubation period. This will cause error in the weight loss of the tea. The other parts of the bag are from plastic and we therefore assume that they do not lose any weight. At the start of the experiment the label (and the rest of the bag) has a very constant weight. You can therefore calculate the start weight of the tea inside the bag by subtracting the standard weight of the bag, rope and label, and the end weight of the tea by subtracting bag weight and rope.

I did not write down the date at which I buried the tea.

Take your best guess, two or three days error does not give us nightmares.

I cannot find my tea bags because my experimental site got destroyed/mown.

That is not nice. Try to find the tea bags and see if they are untouched. If they are above the ground you cannot submit the data. To prevent this, you can make a map specifying distances to things or objects that cannot move. E.g. 2 meter from the tree on the left and 2 meter from the pathway on the right. Placing a stick next to the tea bag and attaching the rope to the stick with a clip may also help to find back the tea bags, but it may also attract people to come and take a look and trample the place.

Researchers questions

How can I calculate k and S?

TBI parameters can be calculated using the sheet on the datasumbission page for more than one datapoint.

If you have more replicates per plot/replicate unit, there are two options. One: you can calculate your TBI parameters pairwise, as we suggest in our calculation sheet. However, it might be that the variation in habitat conditions within your plot occurs at such a small scale that the green and rooibos are not really pairs. In other words, there is the same degree of variation between the pairs as within the pair. If this is the case, you can calculate S using the green teas, average it and use this average S to calculate k, for your separate Rooibos bags.

I cannot calculate k.

The TBI method assumes that rooibos tea is still in the first phase of decomposition while green tea is already in the second phase. With the weight loss of green tea, we calculate which fraction of rooibos tea potentially will break down and together the weight loss of rooibos tea, we calculate how fast the initial decay rate of labile fraction is. Problems to calculate k arise when this assumption is violated. This may mean that your incubation length has been too long, or that decomposition is very fast in your system, by which rooibos tea is no longer in the first, but in the second phase of decomposition. You will than get a negative k or no k at all.

I calculated a negative S.

We assume that during decomposition, the labile fraction of the material will be broken down. S is a measure that quantifies to which degree this fraction is not broken down but stabilizes. A negative S value thus means that breakdown proceeded beyond the labile fraction and that also part of the recalcitrant fraction decomposed.

I got a negative k value.

A negative k value is possible and indicates that your incubation length was probably too long (see the answer of ‘I cannot calculate k‘)

What do you consider labile material?

In our method we assume that every plant material consists of a labile fraction and a recalcitrant fraction. We used sequential extraction to determine these fractions. Sequential extraction determines; the fraction of nonpolar extractive compounds (fats and waxes); of water soluble compounds; of acid soluble compounds; of Acid insoluble compounds and lastly, of mineral compounds by loss on ignition.

The labile fraction is the sum of nonpolar extractives, water and acid soluble compounds.

How can I interpret k and S?

Stabilization (S) is the degree to which litter breaks down, and k is the rate by which this occurs, or to be more precise, the degree and rate by which the labile fraction of the plant material is decomposed.

From a theoretical and mathematical perspective, stabilization (S) can be interpreted as the degree to which the labile fraction of the material is remaining after 3 months of incubation. 1-S thus gives the degree to which the labile fraction has decomposed. It can be that either the half decomposed remains of the labile compounds are too recalcitrant to be broken down in an energetically favorable way given the circumstances, or that the microbial community of that location is not able to deal with certain components in the labile fraction all together. Since the real world is more complex we are aware that not only the labile, but sometimes also the recalcitrant compounds are broken down, and that weight losses can be biased because of growth of bacteria and fungi on the material. Sarah Duddigan from Reading university is breaking new grounds in this and studies the chemical changes in tea during decomposition.

Should I determine the weight of an empty bag?

Yes this is a very good idea!

Should I determine moisture content of the tea?

Yes this is a very good idea, also determine loss by handling when you travel to the field site. However, the latter one is often negligible, especially when you use the box in which it came as travel vessel.

How many replicates I need?

This will depend on the spatial heterogeneity of your site. For citizen scientists we recommend 1 to 3 replicates, whereas researches have to make their own estimations. We usually find more variation in S than in k, but as an example, standard deviations in a Norwegian elevation study were in order of magnitude of 0.02 to 0.06 for S and 0.002 to 0.009 for k (N = 10-12). See also the variation reported in Keuskamp et al. 2013.

Why do you use only one time step?

Traditionally, litter decomposition studies determine decay curves by measuring over several time intervals. Uniquely, the TBI method uses the difference in material composition between green and rooibos tea to obtain two estimates of different phases in the decomposition process. We assume a two phased decomposition model with an initial phase with fast decomposition and a second phase in which further decomposition is negligible. After 3 months, green tea is already in the second phase, and we can estimate to which degree the material is broken down. Than we assume that rooibos tea, corrected for differences in material composition, will decompose to the same degree as green tea (see explanation under ‘What do you consider labile material’). This estimation, combined with the measured decay of rooibos tea allows calculation of the initial decomposition rate. In this way, one can obtain a decay curve with only one measuring point in time.

On the project

How many countries and teabags have been buried so far?

The number of locations and tea bags is growing, please check the list of acknowledgements and the map to see where tea is, and has been buried, respectively. Early 2017 we counted the number of participating location to be around 2000 locations.

When did the project start and how long will it run?

The project started in 2010 and will last at least until 2020.

What is the goal? And Why are you doing it?

We want to create a global map of decomposition, with which we can test our current ideas about the relation between climate and decomposition. Until now, such efforts have been frustrated by lack of comparable data.
We also think that it is important to increase awareness about soil processes and climate change. Even when a citizen scientist did not manage to complete the experiment, we still consider it successful as he or she will still have learned something from it.

What is the relation between TBI 1.0 and TBI 2.0, teatime4science and other tea projects?

The method was picked up enthusiastically in the ecological community which resulted in the initiation of many tea bag experiments. We always like to hear about those initiatives, and welcome contributions to our database from projects that used an unchanged TBI protocol. Projects that are initiated by our team are TBI 1.0, which collects data from the woven bags and TBI2.0 that collects data from the non-woven bags. Teatime4science is the project that was funded by the Swedish Vetenksapsrådet (2015-2018) that enables us to do so. Within Teatime4science we specifically look at effects of climate changes and work with citizen scientists.

What do teabags tell about climate change?

With the tea bags we can measure how much and how fast plant material decomposes. Decomposition is an important step in the carbon cycle which is strongly affecting climate (change). When plant material decomposes the soil will release CO2 and the speed and degree of decomposition will determine how much CO2 is released to the air. As CO2 is a greenhouse gas, the amount of CO2. is important for climate change.

Why is it important to improve climate models?

Because these climate models tell us how we affect the earth and whether we need to take more action to prevent large changes that are harmful for the earth. Until now, many climate models depend on estimated decomposition rates. We want to supply those methods with actual measured data. This was not possible before because methods to measure decomposition required a lot of effort.

Do you have to use this specific tea of Lipton?

Yes, otherwise we cannot compare the results. Other tea types will decay in different ways.

Are you sponsored by Lipton?

No we are not, but we would have nothing against it. We received funding from the Swedish Vetenskapsrådet and the institutes at which we work allow us to spend time on this project, which we are grateful for.