Collected harmonized data on global litter decomposition are of great relevance for scientists, policymakers, and for education of the next generation of researchers and environmental managers. Here we describe the TeaComposition initiative, a global and open research collaborative network to study organic matter decomposition in a standardized way allowing comparison of decomposition rate and carbon turnover across global and regional gradients of ecosystems, climate, soils etc. The TeaComposition initiative today involves 570 terrestrial and 300 aquatic ecosystems from nine biomes worldwide. Further, we describe how to get involved in the TeaComposition initiative by (a) implementing the standard protocol within your study site, (b) joining task forces in data analyses, syntheses and modelling efforts, (c) using collected data and samples for further analyses through joint projects, (d) using collected data for graduate seminars, and (e) strengthening synergies between biogeochemical research and a wide range of stakeholders. These collaborative efforts within/emerging from the TeaComposition initiative, thereby, will leverage our understanding on litter decomposition at the global scale and strengthen global collaborations essential for addressing grand scientific challenges in a rapidly changing world.

Plant community biomass production is co-dependent on climatic and edaphic factors that are often covarying and non-independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan-European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species-specific biomass responses to the environment in the climate-corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co-limited by climatic and soil drivers, with each species experiencing its own unique set of co-limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.

Changes in soil fungal biomass ergosterol, microbial biomass and their role in soil organic carbon (SOC) dynamics along elevation and depth gradients in the Alps are still poorly explored. We investigated changes in stocks of SOC, total N, microbial biomass C (MBC) and N (MBN) and fungal biomass ergosterol at different elevation levels (low, mid and high) in two alpine sites. These two alpine sites represent similar temperature and precipitation regimes, one on alkaline (Hochschwab) the second on acidic (Rauris) bedrock. The stocks of MBC increased with elevation in both sites ranging from 37.6 to 126.1 g m(-2), and MBN stocks from 4.1 to 19.8 g m(-2), following the changes in SOC and total N stocks, except at alkaline low elevation level. The stocks of MBC and MBN were higher at mid-elevation in alkaline than in acidic site. In contrast, MBN stocks were higher at low and high elevation level in acidic site compared to those in alkaline site. Median ergosterol stocks varied around 0.4 g m(-2) in alkaline and increased from 0.05 to 0.2 g m(-2) in acidic site. At all elevation levels, microbial biomass-C/N (MB-C/N) ratio in alkaline site increased with soil depths from 6.0 to 12.3 and remained constant in acidic site between 4.9 and 6.8. In alkaline site, the ratios of ergosterol/MBC declined from 0.6 to 1.4% at 5 cm depth to values around 0.2% at 15-25 cm depth, while this ratio varied between 0.4 and 0.1% at all soil depths in acidic site. In both sites, redundancy and variation partition analysis showed that soil microbial properties were driven by soil chemical properties rather than environmental variables. Our results suggest that environmental variables were less disruptive to soil fungal and microbial biomass and inherent soil properties drive changes in soil microbial and fungal biomass stocks and may drive changes in microbial community structure.

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 degrees C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed. (C) 2018 Elsevier B.V. All rights reserved.

The distribution of microbial biomass and residues and their role in carbon (C) dynamics within soil aggregate fractions in the Alps are still poorly explored. We assessed the distribution of bacterial and fungal residues and their impact on the contribution of the microbial community to C dynamics within soil aggregate size fractions at different elevations. We sampled three sites located at different elevations (1300, 1600 and 2100 m a.s.l.) and subject to different temperature and precipitation regimes in the Central Austrian Alps. Fungal biomass and residues were higher in macro-aggregate fractions compared to micro-aggregates, as indicated by the ratios ergosterol/microbial biomass C and fungal C/bacterial C, suggesting a combined but discrete contribution of fungi and bacterial residues to soil aggregate formation. A greater contribution of microbial residues to soil organic C (SOC) in macro-aggregates demonstrates the importance of microbial residues for the soil organic matter pool's capacity to function as an active nutrient sink and source reservoir. The mid- and low-elevation spruce sites were dominated by fungi and higher aggregate stability, whereas the high-elevation grassland site exhibited a stronger bacterial community as indicated by fungal C/bacterial C ratio. In addition, greater proportions of fungal and bacterial residue in SOC at mid-elevation spruce and high-elevation grassland sites respectively, indicate differential role of fungi and bacteria in SOC sequestration. However, the observed changes in microbial community and residue contribution were mainly driven by variations in soil pH, C/N ratio and fine root biomass. Our findings indicate that fungi played a key role in the internal cycling of SOC and aggregate stability at the mid-elevation spruce site, while bacterial residues were successively activated and contributed increasingly to SOC sequestration at the high-elevation grassland site.

Decomposition of plant litter is a key process for the transfer of carbon and nutrients in ecosystems. Carbon contained in the decaying biomass is released to the atmosphere as respired CO2, and may contribute to global warming. Litterbag studies have been used to improve our knowledge of the drivers of litter decomposition, but they lack comparability because litter quality is plant species-specific. The use of commercial tea bags as a standard substrate was suggested in order to harmonize studies, where green tea and rooibos represent more labile and more recalcitrant C compounds as surrogates of local litter. Here we examine the potential of the use of standardized material for improving our understanding of litter decomposition across climate regions, and to further develop pertinent models. We measured the decomposition of incubated local and standard litters over two years along an elevation gradient in the Austrian Limestone Alps. The similar response to changes in temperature and precipitation of the pairs of local and standard litter—i.e., Fagus sylvatica and green tea, and Pinus nigra and rooibos tea, respectively—suggests the suitability of the standard litters for further examining the role of environmental drivers of decomposition. Harmonized data obtained from standardized litter experiments would provide a key prerequisite for further developing simulation models for the estimation of the C balance of ecosystem litter pools.