The Tea Bag Index (TBI) was designed by Keuskamp et al. (2013) as a standardised and cheap method to quantify microbial-driven decomposition by measuring the mass loss of tea within tea bags. It can be used by scientists and citizen-scientists alike.
However, we found that when the TBI was deployed in tropical forests, termites damaged up to 80% of the tea bags. Termites also consumed the recalcitrant fraction of tea, which is needed to calculate microbial decomposition. In our experiments, TBI estimates could only be retrieved only 20% of the tea bags deployed. This implies that the original TBI cannot be used efficiently in termite-rich tropical ecosystems.
To protect the bags from termites, we tested two methods: physical exclusion with wire mesh and chemical treatment with termite repellent. We found that physical termite-exclusion completely eliminated termite-infringement and hence preserved the full sample size for estimating TBI parameters. Conversely, although chemical treatment was also successful at excluding termites, it inhibited microbial decomposition and made TBI estimates unreliable; therefore, we do not recommend it.
By bench-marking TBI estimates obtained using the original and extended TBI method, and by validation against time-series decomposition data, we found that the microbial decomposition rates predicted in our study were markedly lower than other measurements in tropical and temperate regions. This is a result that we hope will inspire further work.
We propose an extended TBI to measure both microbial and termite effects. Physical termite exclusion can be used on some bags to measure microbial-driven decomposition, and unprotected bags can be used to measure the contribution of termites in driving litter mass loss. By characterising both termite- and microbial-driven decomposition, the extended TBI will provide a comprehensive understanding of decomposition and its drivers in termite-rich ecosystems, and permit meaningful global comparisons.
Read our new paper here:
Teo, A., Kristensen, N.P., Keuskamp, J.A., Evans, T.A., Foo, M., Chisholm, R.A. (2020) Validation and Extension of the Tea Bag Index to Collect Decomposition Data from Termite-rich Ecosystems, Pedobiologia, 80 (pdf)