Evaluating the tea bag method as a potential tool for detecting the effects of added nutrients and their interactions with climate on litter decomposition

Abstract

It is acknowledged that exogenous nutrient addition often stimulates early-stage litter decomposition in forests and late-stage decomposition is generally suppressed by nitrogen addition, whereas the interactive effects of nutrient addition and abiotic environmental factors, such as climate, on decomposition remain unclear. The tea bag method, which was developed to provide the decomposition rate constant k of early-stage decomposition and stabilization factor S of labile materials in the late stage, is a potentially useful tool for examining the impacts of nutrient addition on both early- and late-stage litter decomposition and their interactions with climate. At a long-term (38-year) continuous fertilization experimental site (an Abies sachalinensis Fr. Schmidt stand) in Hokkaido, Japan, we examined whether a standard tea bag method protocol was sufficiently sensitive to reveal any impacts of nutrient addition on early- and late-stage decomposition. In addition, we tested the interactive effects of nutrient addition and climate on litter decomposition. The short incubation period of the tea bag method (ca. 90 days) enabled us to obtain decomposition data from the same location at three different times in a year, i.e., early summer, midsummer, and winter, providing an opportunity to test interactive effects. We demonstrated that the decomposition rate of rooibos tea and the decomposition rate constant k of early-stage decomposition were clearly stimulated by fertilization in midsummer, but no impacts were detected in other seasons, probably because the relative importance of nutrient availability was elevated in midsummer, during which decomposition rates were less constrained by temperature and moisture. The green tea decomposition rate and stabilization factor S, an index related to late-stage decomposition, were unaffected by fertilization. This was probably because the tea bag method does not take into account lignin degradation, which is considered a key factor controlling late-stage litter decomposition. Overall, the present study (i) successfully determined the interactive effects of nutrient addition and climate factors on litter decomposition by making full use of the tea bag method, and (ii) the results suggest that the tea bag method can be a suitable tool for examining the direct effects of nutrient addition and their interactions with environmental factors on early-stage litter decomposition, but not those on late-stage decomposition.

Risk of misinterpreting the Tea Bag Index: Field observations and a random simulation

“…The generated mass loss data of green and rooibos tea are not affected by any environmental factors and contain only observation errors: the mass losses of green and rooibos tea independently follow normal distributions with different means and standard deviations. Therefore, the calculated k and S should not be correlated with each other unless the nonindependence of k and S artificially affects the relationship between k and S. In other words, if any correlations are observed, they are due to artificial effects derived from the nonindependence of k and S. Following Mori, Hashimoto, and Sakai (2021), who observed positive correlations between k and S at a study site, we predicted that k and S are positively correlated.…”

Testing the Tea Bag Index as a potential indicator for assessing litter decomposition in aquatic ecosystems

“…We note that the asymptote model did not fit the real-world data well, and the discrepancy between the two model types may therefore have been overestimated. However, considering that we could not determine S, and that under-or over estimation of S leads to incorrect estimation of k (Mori et al, 2021b), we concluded that the standard protocol used for the TBI method, which was developed in a terrestrial ecosystem, is not applicable to aquatic ecosystems.…”

“…This method uses two types of commercially available tea bags (green and rooibos teas, Lipton) as standard materials to calculate the TBI, which consists of two parameters: a stabilization factor S (the stabilized portion of the hydrolysable fraction during decomposition) and the decomposition constant k of an asymptote model (Keuskamp et al, 2013). Due to its cost-effectiveness and ability to collect comparable globally distributed data (Keuskamp et al, 2013), multiple studies have used the TBI (Becker and Kuzyakov, 2018;Fanin et al, 2020;Fujii et al, 2017;Mori et al, 2021b;Mueller et al, 2018;Petraglia et al, 2019).…”

Effects of Climate and Atmospheric Nitrogen Deposition on Early to Mid-Term Stage Litter Decomposition Across Biomes

“…Our study underlines the importance of considering the effects of different drivers in time and space for a better understanding of litter decomposition processes. Especially analyses of litter chemistry, soil properties, soil biodiversity, and their interactive effects (Mori et al, 2021) on decomposition processes are crucial for improved understanding of this fundamental biogeochemical process.…”