![]() ![]() Using the first assumption, a g can be approximated to the mass loss ratio of green tea at the end of the approximately 90-day incubation. ![]() In the TBI approach, the hydrolysable fractions of green and rooibos teas were divided into unstabilized (i.e., a g and a r, respectively) and stabilized (i.e., 1 − a g and 1 − a r, respectively) fractions. This is possible because the TBI approach assumes that most of the unstabilized hydrolysable fraction of green tea is decomposed within 90 days (the first assumption), and the stabilization factor S (i.e., the ratio of the stabilized to total hydrolysable fractions) of rooibos tea equals that of green tea (second assumption). Namely, time-series data are not required. The TBI approach enables determination of k_TBI and S_TBI using a single pair of mass loss values for the two types of tea during an approximately 90-day incubation ( Figure 1). In the TBI approach, k_TBI is defined as the decomposition constant of an asymptote model describing the decomposition curve of rooibos tea ( Figure 1b), while S_TBI is calculated as the ratio of the stabilized to hydrolysable fractions of green tea. S_TBI was positively correlated with S_fitting, implying that S_TBI can be used as an indicator of S. This study underscores the importance of obtaining time-series data for accurately determining the decomposition constant of an asymptote model describing the decomposition curve of rooibos tea. However, the result showed that k_TBI was negatively correlated with k_fitting. Therefore, this study investigated the positive correlations of k_TBI and S_TBI with k_fitting and S_fitting, respectively, in which case these indexes are useful for comparative analyses. Nevertheless, k_TBI and S_TBI, which can be determined in a cost- and labor-effective manner, might indicate the relative values of k_fitting and S_fitting across different soils and be useful for comparative analyses. However, it was recently revealed that both k_TBI and S_TBI deviate from the actual S and k values accurately determined by fitting an asymptote model to the time series mass of green and rooibos teas remaining ( k_fitting and S_fitting, respectively). k_TBI is defined as the decomposition constant of an asymptote model describing the decomposition curve of rooibos tea, whereas S is the ratio of the stabilized to total hydrolysable fractions of green tea. The Bag Index (TBI) is a novel approach using standardized materials (i.e., commercial tea bags) to evaluate organic matter decomposition by determining two indexes: the early stage decomposition constant k ( k_TBI) and litter stabilization factor S ( S_TBI). ![]()
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