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 °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.

Whereas the NPP and NEP depend largely on an adequate supply of essential plant nutrients (both macro and micro) and available water capacity of the root zone (green water), formation of stable organo-mineral complexes as SOC depends on soil profile characteristics (i.e., depth, horizonation, texture, mineralogical composition, available water capacity, and nutrient reserves) and landscape attributes (i.e., terrain, position, aspect, and drainage). Furthermore, land use (e.g., natural, cropland, grazing land, forest land, urban land, mine land, and wetland) and management (i.e., conservation agriculture [CA], agroforestry, cover cropping, nutrient management, irrigation, crop rotation, farming/cropping system, and

The possibility of carbon (C) being locked away from the atmosphere for millennia is given in hydromorphic soils. However, the water-table-dependent feedback from soil organic matter (SOM) decomposition to the climate system is less clear. At least three greenhouse gases are produced: carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O). These gases show emission peaks at different water table positions and have different global warming potentials (GWP), for example a factor of 23 for CH 4 and 296 for N 2 O as compared with the equivalent mass of CO 2 on a 100-year time horizon. This review of available annual data on all three gases revealed that the radiative forcing effect of SOM decomposition is principally dictated by CO 2 despite its low GWP. Anaerobic SOM decomposition generally has a lower potential feedback to the climatic system than aerobic SOM decomposition. Concrete values are constrained by a lack of data from tropical and subarctic regions. Furthermore, data on N 2 O and on plant effects are generally rare. However, there is a clear latitudinal differentiation for the GWP of soils under anaerobic conditions compared with aerobic conditions when looking at CO 2 and CH 4 : in the tropical and temperate regions, the anaerobic GWP showed a range of 25-60% of the aerobic value, but values varied between 80% and 110% in the boreal zone. Hence, particularly in the vulnerable boreal zone, the feedback from ecosystems to climate change will highly depend on plant responses to changing water tables at elevated temperatures.

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The nations that have ratified the Kyoto Protocol must set up an appropriate national inventory on N2O emissions from agricultural land use, in order to report properly on the achievements made in reducing greenhouse‐gas emissions. The search for the appropriate method is a controversial topic as it is subject to high uncertainty in particular associated to the upscaling from site measurements. In this study, all available data from Germany on annual N2O‐emission rates derived from field experiments of at least an entire year are summarized. From each study, only differences in soil properties on N input qualified as an individual data set. Under these premises, 101 treatments from 27 sites were found equally spread across Germany. The annual N application ranged from 0 to 400 kg N ha–1 and the annual emission rates from 0.04 to 17.1 kg ha–1. Annual emission factors (EFs), uncorrected for background emission, varied considerably from 0.18% to 15.54% of N applied. There was no nationwide correlation found for the relationship between N2O losses and N application, soil C, soil N, soil texture, or soil pH. However, site‐specific trends in the relationship between emission factor and mean soil aeration status, as expressed by the soil type and/or mean climatic conditions, were revealed. Regularly water‐logged soils were characterized by low emission factors as were soils from the drier regions (<600 mm y–1), whereas well‐aerated soils from the frost‐intensive regions showed exceptionally high emission factors. Since purely physical and chemical parameterization failed to describe N2O emissions from agricultural land use on the national scale, there must be a biological adaptation to mean site conditions, i.e., different microbial communities react differently to similar actual conditions in terms of N2O dynamics. Regardless of the point of view, the chapter on N2O soil dynamics cannot be closed yet, and new additional model concepts, process studies, and field measurements are needed.

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