Litter decomposition represents a major path for atmospheric carbon influx into Arctic soils, thereby controlling below-ground carbon accumulation. Yet, little is known about how tundra litter decomposition varies with microenvironmental conditions, hindering accurate projections of tundra soil carbon dynamics with future climate change. Over 14 months, we measured landscape-scale decomposition of two contrasting standard litter types (Green tea and Rooibos tea) in 90 plots covering gradients of micro-climate and -topography, vegetation cover and traits, and soil characteristics in Western Greenland. We used the tea bag index (TBI) protocol to estimate relative variation in litter mass loss, decomposition rate (k) and stabilisation factor (S) across space, and structural equation modelling (SEM) to identify relationships among environmental factors and decomposition. Contrasting our expectations, microenvironmental factors explained little of the observed variation in both litter mass loss, as well as k and S, suggesting that the variables included in our study were not the major controls of decomposer activity in the soil across the studied tundra landscape. We use these unexpected findings of our study combined with findings from the current literature to discuss future avenues for improving our understanding of the drivers of tundra decomposition and, ultimately, carbon cycling across the warming Arctic.

Context The Tea Bag Index (TBI) evaluates the rate of organic matter decomposition using Lipton tea bags. However, this tea bag cannot be easily found in Australia, having to be imported from Europe. The 90-day incubation period also poses problems for school and citizen science projects, such as missing tea bags and organism-induced damage.Aims The study aims to: (1) investigate the suitable alternative Australian tea bag brands for the decomposition studies; (2) assess the potential for reducing the incubation period; and (3) evaluate the priming effects of different substrates on decomposition rate.Methods The feasibility of two local Australian tea bag brands (Madame Flavour or T2) was compared to Lipton by collecting time-series data over the incubation period in pot experiments with the addition of sugar, citric acid and microplastic.Key results We found an alternative tea brand that can be used for TBI in Australia.Conclusions (1) Madame Flavour tea bags can be used as an alternative litter material for the TBI in Australia. (2) The incubation period potentially could be reduced to 21 days, with another sampling taken on day 4 and 14. (3) Although there is a significant difference in decomposition rate between the control and substrates addition, no significant difference in decomposition rate is found among different substrates.Implications The utilisation of the Madame Flavour tea bag enables the adoption of decomposition studies by a broader spectrum of citizen scientists in Australia. More accessible and higher participations in Tea Bag Index (TBI) studies can be achieved by using local tea bag brand. The Madame Flavour tea brand can potentially be used for TBI studies in Australia. The tea incubation period for the TBI method could be shortened down to 21 days.

Tundra soils are one of the world's largest organic carbon stores, yet this carbon is vulnerable to accelerated decomposition as climate warming progresses. The landscape-scale controls of litter decomposition are poorly understood in tundra ecosystems, which hinders our understanding of the global carbon cycle. We examined the extent to which the thermal sum of surface air temperature, soil moisture and permafrost thaw depth influenced litter mass loss and decomposition rates (k), and at which spatial thresholds an environmental variable becomes a reliable predictor of decomposition, using the Tea Bag Index protocol across a heterogeneous tundra landscape on Qikiqtaruk-Herschel Island, Yukon, Canada. We found greater green tea litter mass loss and faster decomposition rates (k) in wetter areas within the landscape, and to a lesser extent in areas with deeper permafrost active layer thickness and higher surface thermal sums. We also found higher decomposition rates (k) on north-facing relative to south-facing aspects at microsites that were wetter rather than warmer. Spatially heterogeneous belowground conditions (soil moisture and active layer depth) explained variation in decomposition metrics at local scales (< 50 m(2)) better than thermal sum. Surprisingly, there was no strong control of elevation or slope on litter decomposition. Our results reveal that there is considerable scale dependency in the environmental controls of tundra litter decomposition, with moisture playing a greater role than the thermal sum at < 50 m(2) scales. Our findings highlight the importance and complexity of microenvironmental controls on litter decomposition in estimates of carbon cycling in a rapidly warming tundra biome.