Abstract
Attempts to obtain standardised decomposition data to determine potential drivers of carbon release have evolved from the use of cotton strips and standardised leaf litter mixtures to the most recent Tea Bag Index (TBI). The TBI is an internationally standardised method to collect comparable, globally distributed data on decomposition rate and litter stabilisation, using commercially available tea bags as standardised test kits. As this index was developed as a citizen science project in the northern hemisphere, we aimed to highlight the potential value – and pitfalls – of its application in a subtropical African savanna. We furthermore aimed to expand on existing protocol details and propose amendments to achieve an enhanced understanding of decomposition dynamics across temporal and spatial scales in African ecosystems. Proposed adaptations include extended incubation periods for long-term monitoring studies, the burial of more tea bags to account for potential losses, and the use of additional equipment to enhance effective sampling. These adaptations provide a system-specific protocol which can facilitate studies aimed to understand the interactions between top-down drivers (e.g. herbivory, fire, climate variability) and bottom-up controls (e.g. decomposition) in carbon flux dynamics of savanna ecosystems. Application of the proposed extended protocol in a semi-arid savanna provided results which reinforce the potential value of the TBI in an African context.
 Significance:
 
 The TBI is a relatively easy and cost-effective approach to gather globally distributed data on potential decomposition rate and inherent carbon flux, yet it was developed and primarily tested in boreal and temperate ecosystems.
 The use of more paired tea bag replicates and additional equipment is a viable means to mitigate tea bag losses to several savanna-based agents of disturbance, while enabling confident conclusions made from statistical results and improved estimates of the TBI. High recovery success across disturbance treatments and incubation periods suggest that the TBI can be applied successfully to spatial and temporal decomposition studies.
Highlights
Research on linkages between decomposition and carbon flux is covered extensively for temperate[1,2] and boreal[3,4] ecosystems, whilst studies in tropical and subtropical ecosystems, especially in Africa, remain limited[5,6]
Attempts to standardise approaches to examine the role of environmental drivers on decomposition have evolved from the use of cotton strips or natural leaf litter mixtures[1,6,9] to the most recent Tea Bag Index (TBI) approach introduced by Keuskamp et al.[8]
Tea bags were selected based upon differences in chemical composition, with green tea representing high-quality organic matter with low C:N ratios, and rooibos tea a low-quality organic matter with high C:N ratios.[3,8,9]
Summary
Research on linkages between decomposition and carbon flux is covered extensively for temperate[1,2] and boreal[3,4] ecosystems, whilst studies in tropical and subtropical ecosystems, especially in Africa, remain limited[5,6]. The paucity of information available on these mechanistic relationships in African savannas may be ascribed to complex interactions between top-down (e.g. climate variability, fire, large mammalian herbivores) and bottom-up controls (e.g. soil physical-chemical properties, soil-based microbes and detritivores) that collectively regulate savanna structure and function.[6,7] While governed by various environmental factors, decomposition is primarily regulated by the chemical composition of site-specific leaf litter. Cross-site comparison of natural litter decomposition and intrinsic drivers thereof is subsequently compromised by variability in detrital chemistry.[1,3,4,6,8,9,10]. Tea bags were selected based upon differences in chemical composition, with green tea representing high-quality organic matter with low C:N ratios, and rooibos tea a low-quality organic matter with high C:N ratios.[3,8,9] Tea bags act as proxies for labile and recalcitrant compounds in naturally occurring organic matter.[1,8,9]
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