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Alpine wetlands, critical ecosystems in high-altitude mountain areas, play essential roles in water conservation, biodiversity protection, and carbon (C) sequestration. These ecosystems are particularly sensitive to climate change, with temperature and precipitation variations significantly impacting their structure and functional processes, such as litter decomposition, a key mechanism for C stabilization. This study focused on the Zoige wetland, a representative alpine wetland located on the eastern edge of the Qinghai-Tibet plateau. An incubation experiment was conducted with soil samples under simulated wet and dry moisture conditions to evaluate the environmental impacts on litter decomposition within this ecosystem. In this study, we employed the Tea Bag Index method, utilizing standardized litter, alongside native litter bags to compare the decomposition processes. This comparison between the uniform composition of standardized litter and the chemically diverse native plant litter aims to provide a comprehensive understanding of litter decomposition dynamics in alpine wetland ecosystems. Our finding showed that both standardized and native litter decomposition significantly decreased under dry conditions, in contrast to wetter condition. The components of both standardized and native litter exhibited a decrease over time, with the easily decomposable fractions breaking down swiftly, in contrast to the slower decomposition of the more resistant components. Furthermore, soil exo-enzyme activities varied significantly with environmental conditions. Wet conditions were observed to enhance soil microbial activity, whereas dry conditions resulted in shifts in microbial biomass C and nitrogen, indicative of drought resilience. The correlation analysis revealed that the composition of native litter is the primary factor influencing its decomposition. In contrast, the decomposition of standardized litter was influenced by both its composition and soil microbial activity. Thus, the distinction between the influences on native and standardized litter decomposition highlights the necessity of considering both litter quality and microbial interaction in ecological studies. This approach offers critical insight into the advantages and limitations of each decomposition methodology within alpine wetland ecosystems.

The Tea Bag Index (TBI) approach is a standardized method for assessing litter decomposition in terrestrial ecosystems. This method allows determination of the stabilized portion of the hydrolysable fraction during the decomposition process, and derivation of a decomposition constant (k) using single measurements of the mass-loss ratios of green and rooibos teas. Although this method is being applied to aquatic systems, it has not been tested if the TBI-based decomposition curves accurately represent the changes in remaining mass of the teas in these environments, where initial leaching tends to be higher than in terrestrial ecosystems. Here, we first tested a critical assumption of the TBI method that green tea decomposition plateaus during the standard incubation period of 90 days, and then tested the accuracy of a TBI-based asymptote model, which was determined using another essential assumption of the TBI approach: the ratio of the decomposable hydrolysable fraction to the total hydrolysable fraction of rooibos tea is the same as that of green tea. Validation data were obtained by incubating tea bags in water samples taken from a stream, a pond, and the ocean in Kumamoto, Japan. We found that green tea decomposition did not plateau during the 90-day period, contradicting a key assumption of the TBI method. The other key assumption was also violated, because the TBI-based asymptote models disagreed with actual decomposition data. Subtracting the leachable fraction from the initial tea mass improved the TBI-based model, but discrepancies with the actual decomposition data remained. Thus, we conclude that the TBI approach, which was developed for a terrestrial environment, is not appropriate for aquatic ecosystems.

The Tea Bag Index (TBI), a novel approach to assessing organic matter decomposition using commercial tea bags, has been increasingly used in academic studies worldwide. This approach was designed to obtain an early-stage decomposition constant (k) indicative of early-stage decomposition rates and a litter stabilization factor (S) indicative of long-term carbon stability by using two types of teas—green and rooibos. However, despite the worldwide usage of the method, the accuracy of this approach has never been validated in terrestrial ecosystems. Here, the validity of this approach was tested by examining the two essential premises of the TBI using a laboratory incubation experiment. The first premise of the TBI—namely, that the unstabilized hydrolyzable fraction of green tea is mostly decomposed within 90 days—did not hold in the present study, which caused overestimations of the S of green tea. The second premise—namely, that the ratio of stabilized to total hydrolyzable fractions (i.e., S) of rooibos tea is equal to that of green tea—was also rejected, which resulted in substantial underestimations of the S of rooibos tea and k. Overall, the TBI largely underestimated the S of rooibos tea and k (more than 1.5 and 5 times smaller than those determined by time-series data, respectively). The present study suggests that time-series mass loss data of rooibos tea should be obtained to accurately determine k, rather than assuming that the S of rooibos tea is equal to that of green tea.

Citizen science is becoming a significant contribution to large scale soil surveys. TeaComposition is a citizen science project introducing the Tea Bag Index (TBI) method to students in Australia to support research on soil decomposition using tea bags (green and rooibos). Soil microbial driven decomposition is an essential soil function that releases soil organic matter (SOM) and nutrients, i.e., soil ecosystem services. The TBI experiments enable citizens to understand this process (increasing soil connectivity) and this information is valuable for assessing urban soil conditions. With 430 TBI in-field incubations between 2017 and 2020, this project engaged more than 3200 students who tested the TBI method on more than 50 school grounds and collected soil samples for analyses of soil properties. Approximately 50% of the tea bags were recovered and mean TBI parameters were: decomposition rate (k) = 0.02 gd−1 and stabilisation factor (S) = 0.32. Soil texture, SOC and SI had the most significant relationships with TBI. Clay and Slaking Index (SI) had negative impacts on k (rs = -0.37, -0.22, p ≤ 0.05, respectively) and SOC had a negative effect for S (rs=-0.27; p ≤ 0.05). These results suggest a combination of high clay and SOC may be related to reduced potential for C sequestration. Regarding citizen science, this study suggests further research using a local tea brand and shorter burials. This suggestion aims to increase Australian citizen participation.

Soils store an important amount of carbon (C), mostly in the form of organic matter in different decomposing stages. Hence, understanding the factors that rule the rates at which decomposed organic matter is incorporated into the soil is paramount to better understand how C stocks will vary under changing atmospheric and land use conditions. We studied the interactions between vegetation cover, climate and soil factors using the Tea Bag Index in 16 different ecosystems (eight forests, eight grasslands) along two contrasting gradients in the Spanish province of Navarre (SW Europe). Such arrangement encompassed a range of four climate types, elevations from 80 to 1420 m.a.s.l., and precipitation (P) from 427 to 1881 mm year -1 . After incubating tea bags during the spring of 2017, we identified strong interactions between vegetation cover type, soil C/N and precipitation affecting decomposition rates and stabilization factors. In both forests and grasslands, increasing precipitation increased decomposition rates (k) but also the litter stabilization factor (S). In forests, however, increasing the soil C/N ratio raised decomposition rates and the litter stabilization factor, while in grasslands higher C/N ratios caused the opposite effects. In addition, soil pH and N also affected decomposition rates positively, but for these factors no differences between ecosystem types were found. Our results demonstrate that soil C flows are altered by complex site-dependent and site-independent environmental factors, and that increased ecosystem lignification will significantly change C flows, likely increasing decomposition rates in the short term but also increasing the inhibiting factors that stabilize labile litter compounds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Grassland ecosystems provide important ecosystem services such as nutrient cycling and primary production that are affected by land-use intensity. To assess the effects of land-use intensity, operational and sensitive ecological indicators that integrate effects of grassland management on ecosystem processes such as organic matter turnover are needed. Here, we investigated the suitability of measuring the mass loss of standardized tea litter together with extracellular enzyme kinetics as a proxy of litter decomposition in the topsoil of grasslands along a well-defined land-use intensity gradient (fertilization, mowing, grazing) in Central Germany. Tea bags containing either green tea (high-quality litter) or rooibos tea (low-quality litter) were buried in 5 cm soil depth. Litter mass loss was measured after three (early-stage decomposition) and 12 months (mid-stage decomposition). Based on the fluorescence measurement of the reaction product 4-methylumbelliferone, Michaelis-Menten enzyme kinetics (V max : potential maximum rate of activity; K m : substrate affinity) of five hydrolases involved in the carbon (C)-, nitrogen (N)- and phosphorus (P)-cycle (β-glucosidase (BG), cellobiohydrolase (CBH), cellotriohydrolase (CTH), 1,4-β-N-acetylglucosaminidase (NAG), and phosphatase (PH)) were determined in tea litter bags and in the surrounding soil. The land-use intensity index (LUI), summarizing fertilization, mowing, grazing, and in particular the frequency of mowing were identified as important drivers of early-stage tea litter decomposition. Mid-stage decomposition was influenced by grazing intensity. The higher the potential activity of all measured C-, N- and P-targeting enzymes, the higher was the decomposition of both tea litters in the early-phase. During mid-stage decomposition, individual enzyme parameters (V max of CTH and PH, K m of CBH) became more important. The tea bag method proved to be a suitable indicator which allows an easy and cost-effective assessment of land-use intensity effects on decay processes in manged grasslands. In combination with enzyme kinetics it is an appealing approach to identify mechanisms driving litter break down., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The Tea Bag Index (TBI) method was used to estimate the litter decomposition rate in peatland exposed for climate manipulation (increased temperature and reduced precipitation) at two contrasting sites differing in water table depth (WTD) dynamics. To manipulate climate on peatland, the prototyped Open Top Chambers (OTC) and automated rain-out shelters were used. OTCs increased daytime air temperatures by ~1.7 °C at the driest plots exposed for an increase of air temperature and reduced precipitation, while the increase of the average daily air temperature was lower than 0.9 °C. However, OTCs cooled down the peat temperature even by 0.8 °C and this effect was most pronounced for daytime rather than night-time conditions. The precipitation amount was reduced by 26%. The tea bags were buried at 8 cm depth for 83 and 172 days starting from the 19th of April 2019. Our observation proved that although decomposition rates were dependent on temperature, WTD and its fluctuations are the main factors controlling the rates of litter decomposition in waterlogged ecosystems like ours. At waterlogged Sphagnum-dominated peatlands, the interrelation between different environmental factors may mitigate the impact of warming and reduced precipitation on litter decomposition., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Salt marshes contribute to climate change mitigation because of their great capacity to store organic matter (OM) in soils. Most of the research regarding OM turnover in salt marshes in times of global change focuses on effects of rising temperature and accelerated sea-level rise, while effects of land-use change have gained little attention. The present work investigates the mechanisms by which livestock grazing can affect OM decomposition in salt marsh soils. In a grazing exclusion experiment at the mouth of the Yangtze estuary, China, we assessed soil microbial exo-enzyme activity (EEA) to gain insight into the microbial carbon (C) and nitrogen (N) demand. Additionally, we studied the decomposition of plant litter in soil using the Tea Bag Index (TBI), a widely used standardized litter bag assay to fingerprint soil decomposition dynamics. Based on EEAs, grazing markedly reduced microbial C acquisition, whereas microbial N acquisition was strongly increased. These opposing grazing effects were also evident in the decomposition of standardized plant litter: The decomposition rate constant (k) and the stabilization (S) of litter were not inversely related, as would be expected, but instead both were reduced by livestock grazing. Our data suggest that gazing effects on EEAs and litter decomposition can just partly be explained by grazing-driven soil compaction and resulting lower oxygen availability, which has previously been hypothesized as a main pathway by which grazing can reduce microbial activity in wetland soils. Instead, grazing effects on microbial nutrient demand occurs to be an at least equally important control on soil decomposition processes., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)