Chemical Underpinning of the Tea Bag Index: An Examination of the Decomposition of Tea Leaves

Abstract

Decomposition is a key flux of terrestrial carbon to the atmosphere. Therefore, gaining a better understanding of how plant litter decomposes in soil, and what governs this process, is vital for global climate models. The Tea Bag Index (TBI) was introduced by Keuskamp et al. (2013) as a novel method for measuring litter decomposition rate and stabilisation. The TBI uses two types of tea bags representing fast (green tea) and slow (rooibos tea) decomposition substrates as standardised litter bags. To date, the TBI method has been used in over 2000 locations across the globe. However, before now, there has been no information on how the composition of the tea leaves change during incubation. These data are crucial in determining the validity of the use of the TBI method globally, to ensure the tea leaves decompose in a way that is representative of so-called “native” litters. To provide chemical underpinning of the TBI method, a laboratory incubation of the tea bags was conducted with destructive sampling at 0, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, and 91 d. The incubated tea was analysed for total C and N. In addition, C was characterised as alkyl, O-alkyl, aromatic, or carbonyl C using solid-state 13C nuclear magnetic resonance spectroscopy with cross-polarization and magic angle spinning (CPMAS NMR). The results suggest that changes in carbon in both tea types are comparable to other litter studies, with a net decrease in total C and relative proportion of O-alkyl C fraction, which contains carbohydrates and cellulose. We conclude that the decomposition of tea leaves in the bags used in the TBI is representative of other litters.

The Tea Bag Index—UK: Using Citizen/Community Science to Investigate Organic Matter Decomposition Rates in Domestic Gardens

“…Decomposition rate is determined from the proportion of rooibos tea that has been decomposed. To decompose the rooibos tea (C:N ratio∼60), microbes will have drawn in N from the surrounding environment [53]. Hence, application of amendments, which increased within garden (z score) N contents and C:N ratio of the soil, will have a significant effect on decomposition rate.…”

“…Although it is unlikely that the tea resembles any of the organic input into these garden systems, use of the TBI will give some indication of the decompositional environment of these garden soils, as determined by management. In addition, decomposition of tea used in the TBI have been found to be representative of other litters [53]. However, there may be some limitations of the use of tea bags associated with the mesh size allowing possible ingrowth of fungal hyphae, effecting results [38].…”

Decomposition of Organic Matter in Caves

“…Because the litter quality is considered as the main driver of decomposition rates at the surface, it is relevant to investigate this in caves where turnover might be affected by a general limitation of labile carbon and nutrient availability. Litter decomposition inside caves might also be influenced by nutrient limitation, because microorganisms can increase the decomposition rate by taking up nitrogen from the surrounding environment (Duddigan et al, 2020), and the oligotrophic conditions inside the cave might decrease the decomposition rate, especially of litter with a high C:N ratio as a result of nitrogen limitation. Hence, differences in the substrate quality might have an even greater influence on decomposition rate inside caves compared to what is observed at the surface.…”

Decomposition and stabilization of the organic matter in an old-growth tropical riparian forest: effects of soil properties and vegetation structure

“…The fraction effectively decomposed and the speed of the decomposition process generally increase with temperature and humidity, stimulating microbial activity (Bradford et al 2016). On the other hand, litter quality is strongly related to the amount of lignin and other recalcitrant compounds (Duddigan et al 2020). High-quality litter is more easily decomposed due to the lower C:N ratio, whereas the decomposition of low-quality litter, with higher amounts of lignin, is slower and may need specialized organisms to be decomposed (Berg 2014), or higher availability of soil nutrients that can be transferred to leaf litter (Bonanomi et al 2017).…”