Tea Bag Index Research Articles

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

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.

Litter decomposition in wet and dry ecosystems of the Brazilian Cerrado

Decomposition of plant litter is a crucial process in carbon and nutrient cycling in all ecosystems, but our understanding of drivers of this process in Brazilian Cerrado (savanna) ecosystems is limited. We determined the decomposition rate and the stabilisation factor in areas of cerrado sensu stricto and palm swamp (vereda) in Bonito de Minas, Minas Gerais, south-eastern Brazil. These two major Cerrado ecosystems differ markedly in environmental conditions, but primarily in water and soil conditions. We used the standardised Tea Bag Index method, characterised soil parameters, and microbial activity to evaluate the decomposition process between these ecosystems. We found higher decomposition rates in the palm swamp compared to cerrado sensu stricto, possibly due to higher soil temperature and humidity conditions and higher microbial biomass.

Ecological responses of semi-natural grasslands to abandonment: case studies in three mountain regions in the Eastern Alps

Semi-natural, extensively managed, grasslands are among the most species-rich agroecosystems in Europe. However, they are threatened by abandonment. We investigated the response of semi-natural grasslands to cessation of mowing at ten sites in three UNESCO Biosphere Reserves in Switzerland and Austria. We assessed vegetation characteristics, topsoil properties and microbially mediated soil processes by comparing once-a-year mowed with adjacent long-term abandoned grasslands on semi-dry, nutrient-poor, base-rich soils. Plant litter decomposition was determined using standardized substrates (Tea Bag Index). Soil microbial community composition was assessed by phospholipid fatty acid analysis. Abandonment altered floristic composition by replacing shade-intolerant or low-growing grassland species, in particular character species of the alliance Bromion erecti, with medium- to tall-sized grasses (e.g. Brachypodium pinnatum) and tall herbs (e.g. Laserpitium latifolium). Time since abandonment had an influence on the magnitude of successional changes after abandonment. Cessation of mowing increased above-ground phytomass but decreased plant species richness and evenness. Abandonment increased soil microbial biomass, promoted litter decomposition and led to an increased soil organic carbon, C:N ratio, and inorganic N supply. Our findings also showed that abandoned grasslands dominated by grasses remained shrub- and treeless for several decades.

An Assessment of the Tea Bag Index Method as a Proxy for Organic Matter Decomposition in Intertidal Environments

AbstractIntertidal wetlands capture and store carbon (C) for long periods of time, helping to reduce the concentration of CO2 in the atmosphere. Yet the processes, which govern the decomposition and subsequent long‐term storage of organic matter (OM) and C in these habitats, remain poorly understood. The Tea Bag Index (TBI) uses a standardized OM (green and Rooibos tea) and has the potential to shed light on OM decomposition across habitats, including saltmarshes. Here, we apply the TBI method at two saltmarshes within the same estuary with the aim of (i) reducing the influence of climatic variables and (ii) determining the role of the environment, including the soil characteristics, in the decomposition of OM. We extended the standard (3 months) incubation period over a full year in order to investigate the longer‐term decomposition processes at each site. The initial results partially support previous studies that the early stages of decomposition (leaching of the water‐soluble fraction) is governed by climatic conditions, but may be further enhanced by tidal flushing in saltmarshes. By extending the incubation period, we observed the initiation of midstage OM decomposition (cellulose degradation) upon which the soil characteristics appear to be the dominant control. These results highlight the importance of long‐term TBI incubations to understand early‐stage OM decomposition. The relationship between tea mass (OM) loss and C loss in these intertidal environments is not straightforward, and we would caution the use of the TBI as a direct universal proxy for soil C degradation in such intertidal wetlands.

Impact of land-use change in mountain semi-dry meadows on plants, litter decomposition and earthworms

Abstract. Traditionally managed mountain grasslands are biodiversity hotspots in central Europe. However, socio-economic trends in agriculture during the last decades have changed farming practices, leaving steep and remote sites abandoned. Especially the abandonment of meadows is well known to directly affect plant and insect diversity. However, not much is known about the effects on soil processes and soil biota. To assess this, we studied four extensively managed (mown once a year, no fertilization) and four abandoned (no mowing, no fertilization) semi-dry meadows in a mountain region in Austria. Plant species richness, plant cover, plant traits, plant biomass, litter decomposition (tea bag index), and earthworm species richness and density were assessed. Additionally, soil temperature, moisture and electrical conductivity were measured. Results showed that managed meadows contained more plant species than abandoned meadows (118 vs. 93 species, respectively). We also observed different plant species assemblages between the two management types. In managed meadows, hemirosette and ruderal plant species were more abundant, while more plant species without rosettes and a higher plant necromass were found in abandoned meadows. Additionally, decomposition rate was higher in abandoned meadows. There was a trend towards higher earthworm densities in managed meadows, but there was no difference in earthworm species richness. We conclude that meadow management has effects on both aboveground vegetation and belowground biota and processes. Both abandoned and extensively managed meadows were important to sustain overall biodiversity and ecosystem functioning in the study region.

How many samples? Soil variability affects confidence in the use of common agroecosystem soil indicators

There is a need for accurate and easily-measured indicators suitable for characterising and monitoring agroecosystem multi-functionality. This is particularly true in intensively-farmed landscapes where it is of interest to quantify the role of small, woody vegetation features in providing ecosystem services such as carbon sequestration. However, soil variability introduced by natural and management processes can interact with sampling designs to result in inappropriate sampling intensities and high levels of uncertainty in measured indicators. This can have consequences for upscaling of ecosystem quantities and decision making. Here, we present results from a pilot study aimed at quantifying and understanding variation in ten common indicators of soil condition and function, within shelterbelt and adjacent field soils, at four dryland sheep farms in Canterbury, New Zealand. Our results demonstrate a high level of spatially-structured soil variability, driven by (1) the effects of woody vegetation on shelterbelt soils relative to field soils, (2) differences in underlying soil types among sites, and (3) possible effects of grazing animals within fields. This soil variability had clear knock-on impacts for appropriate sampling effort, depending on the soil indicator in question, the original soil sampling density, and whether the aim was to estimate population mean values or to detect differences among sites with confidence. On the whole, confidence in soil indicator estimates was highest for soil condition indicators (pH, soil moisture, bulk density), variable for carbon quantities, depending on the measure used, and lowest for soil biological process indicators (tea bag index decomposition rate, bait lamina probe micro-invertebrate activity, and dehydrogenase enzyme activity); estimation confidence was also mostly lower for shelterbelt soils due to the effect of woody roots and inputs on soil variability. Based on our results, we present indicative sample size requirements to estimate population means for these different soil indicators. Ultimately, we advocate for the use of pilot studies, such as the one presented here, to facilitate understanding of variability in soil function indicators within different agroecosystems, and how this variability is partitioned spatially within and among vegetated features.

An affordable and reliable assessment of aquatic decomposition: Tailoring the Tea Bag Index to surface waters

Litter decomposition is a vital part of the global carbon cycle as it determines not only the amount of carbon to be sequestered, but also how fast carbon re-enters the cycle. Freshwater systems play an active role in the carbon cycle as it receives, and decomposes, terrestrial litter material alongside decomposing aquatic plant litter. Decomposition of organic matter in the aquatic environment is directly controlled by water temperature and nutrient availability, which are continuously affected by global change.We adapted the Tea Bag Index (TBI), a highly standardized methodology for determining soil decomposition, for lakes by incorporating a leaching factor. By placing Lipton pyramid tea bags in the aquatic environment for 3 h, we quantified the period of intense leaching which usually takes place prior to litter (tea) decomposition. Standard TBI methodology was followed after this step to determine how fast decomposition takes place (decomposition rate, k1) and how much of the material cannot be broken down and is thus sequestered (stabilization factor, S). A Citizen Science project was organized to test the aquatic TBI in 40 European lakes located in four climate zones, ranging from oligotrophic to hypereutrophic systems. We expected that warmer and/or eutrophic lakes would have a higher decomposition rate and a more efficient microbial community resulting in less tea material to be sequestered.The overall high decomposition rates (k1) found confirm the active role lakes play in the global carbon cycle. Across climate regions the lakes in the warmer temperate zone displayed a higher decomposition rate (k1) compared to the colder lakes in the continental and polar zones. Across trophic states, decomposition rates were higher in eutrophic lakes compared to oligotrophic lakes. Additionally, the eutrophic lakes showed a higher stabilization (S), thus a less efficient microbial community, compared to the oligotrophic lakes, although the variation within this group was high. Our results clearly show that the TBI can be used to adequately assess the decomposition process in aquatic systems. Using “alien standard litter” such as tea provides a powerful way to compare decomposition across climates, trophic states and ecosystems.By providing standardized protocols, a website, as well as face to face meetings, we also showed that collecting scientifically relevant data can go hand in hand with increasing scientific and environmental literacy in participants. Gathering process-based information about lake ecosystems gives managers the best tools to anticipate and react to future global change. Furthermore, combining this process-based information with citizen science, thus outreach, is in complete agreement with the Water Framework Directive goals as set in 2010.

A 30-years vineyard trial: Plant communities, soil microbial communities and litter decomposition respond more to soil treatment than to N fertilization

Soil management strategies in viticulture should not only aim to optimize yield and quality of grapevines, but also sustain soil biodiversity and soil functioning. Here, we report on the combined effects of soil treatment and nitrogen fertilization on parameters related to soil fertility and litter decomposition, as well as plant, fungal, and bacterial communities in a long-term vineyard experiment, where these management practices have been applied since 1987. Plots in this vineyard (Hesse, Germany) were treated with different yearly amounts of nitrogen fertilizer (0, 30, 60, 90, 120, and 150 kg N ha−¹) with two types of inter-row soil treatment (tillage vs. permanent cover). We analyzed soil properties of the topsoil, decomposition parameters using the Tea Bag Index approach, the inter-row plant community, and microbial communities (bacteria and fungi) by next generation sequencing techniques.Long-term tillage decreased soil carbon and nitrogen levels as well as some plant available nutrients, whereas soil pH and plant available phosphorus increased. Elevated amounts of nitrogen fertilization slightly increased soil carbon and nitrogen levels. Relative mass loss of tea bag content due to decomposition was decreased, while stabilization of labile litter components was increased by tillage, compared to permanent cover treatments. Plant community patterns were changed by soil treatment with tillage inter-rows exhibiting annual, ruderal species and being more diverse compared to permanent cover inter-rows. Relative abundance of several bacterial phyla and fungal orders responded strongly to soil treatment. Changes in soil pH and levels of phosphorus could partly explain the underlying mechanisms involved in shifts of bacterial and fungal communities, respectively. In contrast, long-term nitrogen fertilization only slightly shifted plant and microbial community composition. This study shows that over the long-term, soil treatment strongly affects soil functioning and biodiversity, exceeding the effect of even high nitrogen fertilization levels.

Litter decomposition: effects of temperature driven by soil moisture and vegetation type

We examined the importance of litter quality and microclimate on early-stage litter mass loss, analysed the importance of interactions among environmental factors in determining key decomposition parameters and compared the variation in decomposition rates in vegetation types and sites with similar climate. Following the Tea-Bag Index approach, 464 tea-bags were incubated in the soil in 79 sites, distributed across Italy, which included six vegetation types and a broad range of microclimatic conditions. Litter type exerted a stronger control on mass loss compared to climatic factors. The effects of soil moisture were not the same for high and lower quality litter. In addition, the effects of temperature on the decomposition rate depended on soil moisture. The stabilization factor was strongly temperature-dependent, but the influence of temperature differed among vegetation types: those dominated by small-size plants showed a strong decrease in the potential amount of plant material entering into the soil stock under warmer temperatures. The lowest variation in decomposition rate was found in sites characterised by low temperatures, and, among the vegetation types, in alpine snowbeds. The role of litter quality and of the interactions among environmental conditions can potentially determine significant shifts in the expected patterns of ecosystem carbon fluxes.

Stabilization versus decomposition in alpine ecosystems of the Northwestern Caucasus: The results of a tea bag burial experiment

Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the local carbon cycle: litter decomposition and carbon stabilization. In order to adequately reflect local heterogeneity, we have sampled 12 typical plant communities of the Russian Caucasus. In order to minimize confounding effects and encourage comparative studies, we have adapted the widely used tea bag index (TBI) that is typically used in areas with low decomposition. By incubating standardized tea litter for a year, we investigated whether (1) initial litter decomposition rate (k) is negatively correlated with litter stabilization (S) and (2) whether k or S exhibit correlations with altitude and other environmental conditions. Our results show that S and k are not correlated. Altitude, pH, and water content significantly influenced the stabilization factor S, while soil-freezing had no influence. In contrast, none of these factors predicted the decomposition rate k. Based on our data, we argue that collection of decomposition rates alone, as is now common practice, is not sufficient to understand carbon input to soils and can potentially lead to misleading results. Our data on community-specific decomposition and stabilization rates further constrain estimates of litter accumulation in subalpine communities and the potential effects of climate change.

Teatime on Mount Kilimanjaro: Assessing climate and land‐use effects on litter decomposition and stabilization using the Tea Bag Index

AbstractDecomposition is one of the most important processes in ecosystem carbon (C) and nutrient cycles and is a major factor controlling ecosystem functions. The functioning of Afromontane ecosystems and their ability to provide ecosystem services are particularly threatened by climate and land‐use change. Our objectives were to assess the effects of climatic conditions (elevation and seasonality) and land‐use intensity on litter decomposition and C stabilization in 10 ecosystems along the unique 3,000‐m elevation gradient of Mt. Kilimanjaro.Tea Bag Index parameters (decomposition‐rate‐constant k and stabilization‐factor S) were used to quantify decomposition of standardized litter substrate. Nine pairs of tea bags (green and rooibos tea) were exposed in each ecosystem during the short‐wet, warm‐dry, long‐wet and cold‐dry season.Decomposition rate increased from k = 0.007 in savanna (SAV; 950‐m elevation), up to a maximum of k = 0.022 in montane cloud forest (2,100 m). This was followed by a 50% decrease in (sub‐)alpine ecosystems (>4,000 m). SAV experienced the strongest seasonal variation, with 23‐times higher S values in dry season compared with wet season. The conversion of SAV to maize monocultures (~1,000 m) and traditional agroforestry to large‐scale coffee plantations (~1,300 m) increased mean k values, and stabilization factors were about one‐third lower.Forests between 1,900 and 2,100 m represent the zone of sufficient moisture and optimal temperature conditions. Seasonal moisture (lower slope) and temperature limitation (alpine zone) decreases litter decomposition. Mt. Kilimanjaro ecosystems are highly sensitive to land‐use change, which accelerates ecosystem cycles and decreases C stabilization.

Long-Term Climate Regime Modulates the Impact of Short-Term Climate Variability on Decomposition in Alpine Grassland Soils

Decomposition of plant litter is an important process in the terrestrial carbon cycle and makes up approximately 70% of the global carbon flux from soils to the atmosphere. Climate change is expected to have significant direct and indirect effects on the litter decomposition processes at various timescales. Using the TeaBag Index, we investigated the impact on decomposition of short-term direct effects of temperature and precipitation by comparing temporal variability over years, versus long-term climate impacts that incorporate indirect effects mediated through environmental changes by comparing sites along climatic gradients. We measured the initial decomposition rate (k) and the stabilization factor (S; amount of labile litter stabilizing) across a climate grid combining three levels of summer temperature (6.5–10.5°C) with four levels of annual precipitation (600–2700 mm) in three summers with varying temperature and precipitation. Several (a)biotic factors were measured to characterize environmental differences between sites. Increased temperatures enhanced k, whereas increased precipitation decreased k across years and climatic regimes. In contrast, S showed diverse responses to annual changes in temperature and precipitation between climate regimes. Stabilization of labile litter fractions increased with temperature only in boreal and sub-alpine sites, while it decreased with increasing precipitation only in sub-alpine and alpine sites. Environmental factors such as soil pH, soil C/N, litter C/N, and plant diversity that are associated with long-term climate variation modulate the response of k and S. This highlights the importance of long-term climate in shaping the environmental conditions that influences the response of decomposition processes to climate change.

Alteration of soil properties by the invasive tree Psidium cattleianum along a precipitation gradient on O'ahu Island, Hawai'i

To test the effects of invasion by strawberry guava trees (Psidium cattleianum) on the forest soil ecosystem, we compared soil properties between pairs of adjacent native and P. cattleianum stands. We set up six study sites that had developed under different mean annual precipitation levels in the Ko'olau Mountains on the island of O'ahu, Hawai'i. Accumulated litter mass and soil pH decreased with precipitation in the native stands. Invasion by P. cattleianum increased the amount of litter and reduced the differences in soil water content and pH among the sites. We compared the decomposition process using the Tea Bag Index, which is determined by the difference in dry mass of commercially available green and rooibos teas in nylon mesh bags before and after 90 days of burial. Psidium cattleianum increased the initial litter decomposition rate irrespective of precipitation and other soil properties. On the other hand, P. cattleianum increased the long-term litter stabilization factor of the Tea Bag Index in wetter sites. The accumulation of litter was likely caused by indirect effects of P. cattleianum through the alteration of soil moisture properties. In summary, this study shows that invasion by P. cattleianum could alter the soil properties in both wet and mesic sites, suggesting the possibility of change in composition and/or function of decomposers.

Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems

Summary Changes in the balance between soil carbon storage and release can significantly amplify or attenuate global warming. Although a lot of progress has been made in determining potential drivers of carbon release through large‐scale decomposition experiments, climate predictions are still hampered by data limitation at a global scale as a result of high effort and measurement costs of comparative litter decomposition studies. We introduce an innovative, cost‐effective, well‐standardised method to gather data on decomposition rate and litter stabilisation using commercially available tea bags as standardised test kits. By using two tea types with contrasting decomposability, we can construct a decomposition curve using a single measurement in time. The acquired Tea Bag Index (TBI) consists of two parameters describing decomposition rate (k) and litter stabilisation factor (S). The method was tested for its sensitivity and robustness in contrasting ecosystems and biomes, confirming that the TBI is sensitive enough to discriminate between these systems. Within an ecosystem, TBI is responsive to differences in abiotic circumstances such as soil temperature and moisture content. The collected k and S values are in accordance with expectations based on decomposition process literature. They are therefore interpretable within the current knowledge framework. Tea Bag Index is a unique, multifunctional method requiring few resources and minimal prior knowledge. The standardisation and simplicity of the method make it possible to collect comparable, globally distributed data through crowdsourcing. TBI can further provide an excellent decomposition reference and has the potential to increase reliability of soil carbon flux estimates based on extrapolations of decomposition data.