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Abstract: Data sets of biometeorological measurements of ecosystem CO2 flux, combined with harvest and manure data from several European cropland were integrated to provide an assessment of the carbon budget. Sites encompassed different climatic regions and contrasting crop rotations. The influence of different crops and management practices was also assessed to identify some of the major factors contributing to the cropland carbon balance. Since crops are rotated and cropping periods do not always follow the calendar year, net ecosystem production (NEP) as well as net biome production (NBP) sums of full crop rotations or of at least 4 years of longer-term crop rotations and of monocultures were used. In a second analysis NBP sums were correlated to soil properties. Finally, the data were combined with additional data to derive a mean annual GHG balance for the European cropland sites under consideration. Five crop rotations and two monocultures were integrated over 4 years. During 4 years the average annual NEP was −240±113gCm−2 y−1. On average, 382±117gCm−2 y−1 were harvested, where as average carbon inputs by manure and seeding was 47±51gCm−2 y−1. The average NBP of the seven sites under consideration was estimated to be a carbon loss of 95±87gCm−2 y−1. The full GHG balance of the considered sites was estimated to be 160gCm−2 y−1 in CO2-equivalents. These results challenge current good practice guidelines that predict neutral carbon budgets for systems where the inputs of manure and crop residues are of comparable magnitude to those associated with the sites examined in this study. Ongoing humus loss in spite of good practice is mainly related to soils with high carbon concentrations which are not in equilibrium but may also be a result of already ongoing climate change. A modification in the good practice guidelines to increase carbon inputs may be required. Results from a representativeness analysis suggest that more than 50 sites are necessary for a European cropland flux network to adequately represent the variability of climate, soil and management within the European continent. Thus, the uncertainties due to the network design are currently bigger than the uncertainty intrinsic in the measurement method. [Copyright &y& Elsevier]

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006--winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44° to 62°N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m-2 anomaly compared with the decadal mean over the January--May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m-2 anomaly over 5 months), leading to higher net uptake than the long-term mean at all sites (+12 to +79 gC m-2 anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process-based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation. [ABSTRACT FROM AUTHOR]

The European CARBOEUROPE/FLUXNET monitoring sites, spatial remote sensing observations via the EOS-MODIS sensor and ecosystem modelling provide independent and complementary views on the effect of the 2003 heatwave on the European biosphere's productivity and carbon balance. In our analysis, these data streams consistently demonstrate a strong negative anomaly of the primary productivity during the summer of 2003. FLUXNET eddy-covariance data indicate that the drop in productivity was not primarily caused by high temperatures (‘heat stress’) but rather by limitation of water (drought stress) and that, contrary to the classical expectation about a heat wave, not only gross primary productivity but also ecosystem respiration declined by up to more than to 80 gC m−2 month−1. Anomalies of carbon and water fluxes were strongly correlated. While there are large between-site differences in water-use efficiency (WUE, 1–6 kg C kg−1 H2O) here defined as gross carbon uptake divided by evapotranspiration (WUE=GPP/ET), the year-to-year changes in WUE were small (<1 g kg−1) and quite similar for most sites (i.e. WUE decreased during the year of the heatwave). Remote sensing data from MODIS and AVHRR both indicate a strong negative anomaly of the fraction of absorbed photosynthetically active radiation in summer 2003, at more than five standard deviations of the previous years. The spatial differentiation of this anomaly follows climatic and land-use patterns: Largest anomalies occur in the centre of the meteorological anomaly (central Western Europe) and in areas dominated by crops or grassland. A preliminary model intercomparison along a gradient from data-oriented models to process-oriented models indicates that all approaches are similarly describing the spatial pattern of ecosystem sensitivity to the climatic 2003 event with major exceptions in the Alps and parts of Eastern Europe, but differed with respect to their interannual variability. [ABSTRACT FROM AUTHOR]

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr-1) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes. [ABSTRACT FROM AUTHOR]

Abstract. This paper responds to the Forum contribution by Piovesan & Adams (2000) who criticized the results obtained by the EUROFLUX network on carbon fluxes of several European forests. The major point of criticism was that the data provided by EUROFLUX are inconsistent with current scientific understanding. It is argued that understanding the terrestrial global carbon cycle requires more than simply restating what was known previously, and that Piovesan & Adams have not been able to show any major conflicts between our findings and ecosystem or atmospheric-transport theories. [ABSTRACT FROM AUTHOR]

Abstract: The greenhouse gas budgets of 15 European crop sites covering a large climatic gradient and corresponding to 41 site-years were estimated. The sites included a wide range of management practices (organic and/or mineral fertilisation, tillage or ploughing, with or without straw removal, with or without irrigation, etc.) and were cultivated with 15 representative crop species common to Europe. At all sites, carbon inputs (organic fertilisation and seeds), carbon exports (harvest or fire) and net ecosystem production (NEP), measured with the eddy covariance technique, were calculated. The variability of the different terms and their relative contributions to the net ecosystem carbon budget (NECB) were analysed for all site-years, and the effect of management on NECB was assessed. To account for greenhouse gas (GHG) fluxes that were not directly measured on site, we estimated the emissions caused by field operations (EFO) for each site using emission factors from the literature. The EFO were added to the NECB to calculate the total GHG budget (GHGB) for a range of cropping systems and management regimes. N2O emissions were calculated following the IPCC (2007) guidelines, and CH4 emissions were estimated from the literature for the rice crop site only. At the other sites, CH4 emissions/oxidation were assumed to be negligible compared to other contributions to the net GHGB. Finally, we evaluated crop efficiencies (CE) in relation to global warming potential as the ratio of C exported from the field (yield) to the total GHGB. On average, NEP was negative (−284±228gCm−2 year−1), and most cropping systems behaved as atmospheric sinks, with sink strength generally increasing with the number of days of active vegetation. The NECB was, on average, 138±239gCm−2 year−1, corresponding to an annual loss of about 2.6±4.5% of the soil organic C content, but with high uncertainty. Management strongly influenced the NECB, with organic fertilisation tending to lower the ecosystem carbon budget. On average, emissions caused by fertilisers (manufacturing, packaging, transport, storage and associated N2O emissions) represented close to 76% of EFO. The operation of machinery (use and maintenance) and the use of pesticides represented 9.7 and 1.6% of EFO, respectively. On average, the NEP (through uptake of CO2) represented 88% of the negative radiative forcing, and exported C represented 88% of the positive radiative forcing of a mean total GHGB of 203±253g C-eqm−2 year−1. Finally, CE differed considerably among crops and according to management practices within a single crop. Because the CE was highly variable, it is not suitable at this stage for use as an emission factor for management recommendations, and more studies are needed to assess the effects of management on crop efficiency. [Copyright &y& Elsevier]