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.

-Our objective was to quantify the annual soil carbon efflux in a young beech forest in north-eastern France (Hesse Forest, Euroflux site FR02) from measurements of soil CO, efflux. Soil CO, efflux exhibited pronounced seasonal variations which did not solely reflect seasonal changes in soil temperature. In particular, strong differences in soil CO, efflux were observed between summer 1996 and summer 1997 while the patterns of soil temperature were similar. This difference is at least partly explained by an inhibition of soil CO, efflux at low soil water content. Since changes in soil temperature (T) and soil volumetric water content at -10 cm (&thetas; v ) affect soil CO 2 efflux, an empirical model is proposed (y = A q v e BT ) which account for 86 % of the variation in soil CO, efflux

Summary1. We present measurements of CO 2 fluxes over 2 years above and within a young Beech stand in the east of France. This site is part of the Euroflux network set up to monitor fluxes over representative European forests. 2. The net ecosystem carbon (C) exchange was derived from continuous eddy flux measurements. Major components of the total flux (i.e. soil and above-ground biomass respiration and assimilation of leafy branches) were measured independently using chambers. The main C stocks (i.e. root, stem and branch biomass) were also quantified. 3. Daily minima of CO 2 flux were typically around -20 µ mol CO 2 m -2 s -1 during the period of full leaf expansion, while night-time ecosystem respiration varied between 5 and 15 µ mol CO 2 m -2 s -1. The seasonal pattern of net ecosystem assimilation was very close to that of net assimilation at the single branch scale. The seasonal variation of net ecosystem exchange was closely related to leaf expansion and soil water content during the dry year of 1996. 4. Measurements of ecosystem respiration (eddy flux) were corrected for CO 2 storage within the stand. This C flux showed a seasonal pattern, the maximum rates (4-7 g C m -2 day -1 ) occurring in spring and summer, and appeared to be correlated with soil temperature. Temporal variation of soil respiration showed the same pattern, and effects of both temperature and soil drying were found. Annual soil respiration was ≈ 70% of ecosystem respiration. Root respiration was 60% of the total below-ground respiration. 5. Annual net C exchange was -218 and -257 g C m -2 in 1996 and 1997, respectively, corresponding to net C uptake by the forest. These values are much lower than the annual biomass increment (stems and large roots) of the stand: 427 and 471 g C m -2 year -1 , respectively. The difference may be explained by a release of CO 2 from the decomposition of woody debris. 6. Ecosystem C loss by respiration was 800-1000 g C m -2 year -1 . Gross C gain was 1000-1300 g C m -2 year -1 . Ecosystem respiration therefore played a major role in the annual C balance of this forest.

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