Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems

<jats:title>Summary</jats:title><jats:p> <jats:list> <jats:list-item><jats:p>Changes in the balance between soil carbon storage and release can significantly amplify or attenuate global warming. Although a lot of progress has been made in determining potential drivers of carbon release through large‐scale decomposition experiments, climate predictions are still hampered by data limitation at a global scale as a result of high effort and measurement costs of comparative litter decomposition studies.</jats:p></jats:list-item> <jats:list-item><jats:p>We introduce an innovative, cost‐effective, well‐standardised method to gather data on decomposition rate and litter stabilisation using commercially available tea bags as standardised test kits. By using two tea types with contrasting decomposability, we can construct a decomposition curve using a single measurement in time. The acquired <jats:styled-content style="fixed-case">T</jats:styled-content>ea <jats:styled-content style="fixed-case">B</jats:styled-content>ag <jats:styled-content style="fixed-case">I</jats:styled-content>ndex (<jats:styled-content style="fixed-case">TBI</jats:styled-content>) consists of two parameters describing decomposition rate (<jats:italic>k</jats:italic>) and litter stabilisation factor (<jats:italic><jats:styled-content style="fixed-case">S</jats:styled-content></jats:italic>).</jats:p></jats:list-item> <jats:list-item><jats:p>The method was tested for its sensitivity and robustness in contrasting ecosystems and biomes, confirming that the <jats:styled-content style="fixed-case">TBI</jats:styled-content> is sensitive enough to discriminate between these systems. Within an ecosystem, <jats:styled-content style="fixed-case">TBI</jats:styled-content> is responsive to differences in abiotic circumstances such as soil temperature and moisture content. The collected <jats:italic>k</jats:italic> and <jats:italic><jats:styled-content style="fixed-case">S</jats:styled-content></jats:italic> values are in accordance with expectations based on decomposition process literature. They are therefore interpretable within the current knowledge framework.</jats:p></jats:list-item> <jats:list-item><jats:p>Tea Bag Index is a unique, multifunctional method requiring few resources and minimal prior knowledge. The standardisation and simplicity of the method make it possible to collect comparable, globally distributed data through crowdsourcing. <jats:styled-content style="fixed-case">TBI</jats:styled-content> can further provide an excellent decomposition reference and has the potential to increase reliability of soil carbon flux estimates based on extrapolations of decomposition data.</jats:p></jats:list-item> </jats:list> </jats:p>