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

Identifying potential threats to soil biodiversity

A decline in soil biodiversity is generally considered to be the reduction of forms of life living in soils, both in terms of quantity and variety. Where soil biodiversity decline occurs, it can significantly affect the soils’ ability to function, respond to perturbations and recover from a disturbance. Several soil threats have been identified as having negative effects on soil biodiversity, including human intensive exploitation, land-use change and soil organic matter decline. In this review we consider what we mean by soil biodiversity, and why it is important to monitor. After a thorough review of the literature identified on a Web of Science search concerning threats to soil biodiversity (topic search: threat* “soil biodiversity”), we compiled a table of biodiversity threats considered in each paper including climate change, land use change, intensive human exploitation, decline in soil health or plastic; followed by detailed listings of threats studied. This we compared to a previously published expert assessment of threats to soil biodiversity. In addition, we identified emerging threats, particularly microplastics, in the 10 years following these knowledge based rankings. We found that many soil biodiversity studies do not focus on biodiversity sensu stricto, rather these studies examined either changes in abundance and/or diversity of individual groups of soil biota, instead of soil biodiversity as a whole, encompassing all levels of the soil food web. This highlights the complexity of soil biodiversity which is often impractical to assess in all but the largest studies. Published global scientific activity was only partially related to the threats identified by the expert panel assessment. The number of threats and the priority given to the threats (by number of publications) were quite different, indicating a disparity between research actions versus perceived threats. The lack of research effort in key areas of high priority in the threats to soil biodiversity are a concerning finding and requires some consideration and debate in the research community

A comparison of physical soil organic matter fractionation methods for amended soils

Selecting a suitable physical fractionation method, to investigate soil organic matter dynamics, from the plethora that are available is a difficult task. Using five different physical fractionation methods, on soils either nontreated or with a history of amendment with a range of exogenous organic matter inputs (Irish moss peat; composted horse manure; garden compost) and a resulting range of carbon contents (6.8 to 22.2%), we show that method selection had a significant impact on both the total C recovered and the distribution of the recovered C between unprotected, physically protected, or chemically protected conceptual pools. These between-method differences most likely resulted from the following: (i) variation in the methodological fractions obtained (i.e., distinguishing between aggregate size classes); (ii) their subsequent designation to conceptual pools (e.g., protected versus unprotected); and (iii) the procedures used in sample pretreatment and subsequent aggregate dispersion and fractionation steps. The performance of each method also varied depending on the amendment in question. The findings emphasise the need for an understanding of the nature of the soil samples under investigation, and the stabilisation mechanism of interest, both prior to method selection and when comparing and interpreting findings from literature studies using different fractionation methods

The extent and applications of metal accumulation and hyperaccumulation in Philippine plants

To examine the potential applications of hyperaccumulator plants in the Philippines we reviewed current data on the extent of metal hyperaccumulation in native species, and partitioning of metals within the plant tissue. Twenty-eight species had reported tissue concentrations above the hyperaccumulator threshold, eleven species were endemic to the Philippines. Nickel was present in higher concentrations in the aboveground tissue than the belowground tissue, but the reverse was found for copper, aluminium, and chromium. The fact that copper accumulates belowground rather than above, and most hyperaccumulators of nickel identified were trees has implications for the potential of phytoextraction using native Philippines flora

Effects of repeated application of organic soil amendments on horticultural soil physicochemical properties, nitrogen budget and yield

Application of organic amendments to soil is commonplace in domestic gardening. However, a vast array of materials could be labelled as ‘compost’ by retailers and suppliers. We investigated six different amendments currently used, or available for use, in horticulture: composted bark, composted bracken, spent mushroom compost, composted horse manure, garden waste compost (at two different application rates), and peat. Using a controlled field experiment, we examined the physicochemical differences between the amendments, the subsequent effects on soil characteristics, and resultant yield and biometrics of Lavatera trimiestris. Amended soils resulted in a significantly different multivariate soil environment and N budget when compared to the unamended control. However, the effect on yield and plant biometrics (number of flowers, plant height, etc.) depended on the amendment used. Application of garden compost resulted in up to a five-fold increase in yield. However, there was no significant difference in yields in soils amended with composted bark or peat, when compared to the unamended control. This has implications, as there is increasing pressure to remove peat from products available to domestic gardeners. The variability in the different amendments investigated in our research, in addition to the variable effects on plant growth parameters, suggests that repeated use of a single amendment may not be best practise for gardeners

Optimizing pH for soil enzyme assays reveals important biochemical functions in low pH soil

Soil enzyme assays are often used as indicators of potential biological functions. The objective of this study was to understand enzyme activity across a range of soil pH. Soils (0–15 cm) were collected from a heathland restoration project (established 1999) on the Isle of Purbeck, UK with treatments of elemental sulphur or ferrous sulphate compared to a control, acid grassland and heathland. Enzyme assays were conducted using fluorescent substrates for β-1,4-glucosidase, β-N-acetylglucosaminidase (NAG) and phosphatase with a range of buffer pH from 3.0 to 12.0. Differences in soil pH were still evident with the control (pH 5.3) and ferrous sulphate (pH 5.2) significantly higher than elemental sulphur (pH 4.5), acid grassland (pH 4.3) and heathland (pH 4.0). The optimum buffer pH for enzyme assays varied from pH 3-4.5 for β-glucosidase, pH 4–5 for NAG and pH 4–6 for phosphatase. Comparisons using a standard MUB pH resulted in different conclusions compared to optimum pH. For example, β-glucosidase activity at pH 5 for the control was significantly higher than elemental sulphur, acid grassland, and heathland. However, there were no differences when the pH optimums were considered. Comparisons of phosphatase activity at MUB pH 6.5 resulted in higher activity in the control plots compared to the heathland, despite the heathland soils showing the highest activity at optimum buffer pH. By examining the relationships between soil pH, enzyme activity, and assay conditions, this study highlights the importance of optimizing pH in enzyme assays when comparing diverse soil types

The Tea Bag Index—UK: using citizen/community science to investigate organic matter decomposition rates in domestic gardens

Gardening has the potential to influence several ecosystem services, including soil carbon dynamics, and shape progression towards the UN Sustainable Development Goals, (e.g., SDG 13). There are very few citizen/community science projects that have been set up to test an explicit hypothesis. However, citizen/community science allows collection of countrywide observations on ecosystem services in domestic gardens to inform us on the effects of gardening on SDGs. The geographical spread of samples that can be collected by citizen/community science would not be possible with a team of professional science researchers alone. Members of the general public across the UK submitted soil samples and buried standardised litter bags (tea bags) as part of the Tea Bag Index—UK citizen/community science project. Participants returned 511 samples from across the UK from areas in their garden where soil organic amendments were and were not applied. The project examined the effects of application of soil amendments on decomposition rates and stabilisation of litter, and in turn, effects on soil carbon and nitrogen concentrations. This was in response to a call for contributions to a global map of decomposition in the Teatime4Science campaign. Results suggested that application of amendments significantly increased decomposition rate and soil carbon, nitrogen, and carbon: nitrogen ratios within each garden. So much so that amendment application had more influence than geographic location. Furthermore, there were no significant interactions between location and amendment application. We therefore conclude that management in gardens has similar effects on soil carbon and decomposition, regardless of the location of the garden in question. Stabilisation factor was influenced more prominently by location than amendment application. Gardening management decisions can influence a number of SDGs and a citizen/community science project can aid in both the monitoring of SDGs, and involvement of the public in delivery of SDG

Reasons to not correct for leaching in TBI; Reply to Lind et al. (2022)

We believe that correcting for leaching in (terrestrial) litterbags studies such as the Tea Bag Index will result in more uncertainties than it resolves. This is mainly because leaching occurs in pulses upon changes in the environment and because leached material can still be mineralized after leaching. Furthermore, amount of material that potentially leaches from tea is comparable to other litter types. When correcting for leaching, it is key to be specific about the employed method, just like being specific about the study specific definition of decomposition

Impact of zero budget natural farming on crop yields in Andhra Pradesh, SE India

It has been claimed that Zero Budget Natural Farming (ZBNF), a burgeoning practice of farming in India based on low-inputs and influenced by agro-ecological principles, has the potential to improve farm viability and food security. However, there is concern that the success of the social movement fueling the adoption of ZBNF has become out of step with the science underpinning its performance relative to other farming systems. Based on twenty field plot experiments established across six districts in Andhra Pradesh (SE India), managed by locally based farmer researchers, we present the first ‘on the ground’ assessment of ZBNF performance. We show that there is no short-term yield penalty when adopting ZBNF in small scale farming systems compared to conventional and organic alternatives. In terms of treatment response, we observed differences between agro-climatic zones, but in this initial evaluation we cannot recommend specific options tuned to these different contexts