Full accounting of the greenhouse gas (CO2, N2O, CH4) budget of nine European grassland sites.

The full greenhouse gas balance of nine contrasted grassland sites covering a major climatic gradient over Europe was measured during two complete years. The sites include awide range ofmanagement regimes (rotational grazing, continuous grazing andmowing), the three main types of managed grasslands across Europe (sown, intensive permanent and semi-natural grassland) and contrasted nitrogen fertilizer supplies. At all sites, the net ecosystem exchange (NEE) of CO2 was assessed using the eddy covariance technique.N2Oemissions weremonitored using various techniques (GC-cuvette systems, automated chambers and tunable diode laser) and CH4 emissions resulting from enteric fermentation of the grazing cattle were measured in situ at four sites using the SF6 tracer method. Hence, when expressed in CO2-C equivalents, emissions of N2O and CH4 resulted in a 19% offset of the NEE sink activity. An attributedGHG balance has been calculated by subtracting fromthe NBP: (i)N2OandCH4 emissions occurring within the grassland plot and (ii) off-site emissions ofCO2 andCH4 as a result of the digestion and enteric fermentation by cattle of the cut herbage.The net exchanges by the grassland ecosystems of CO2 and of GHG were highly correlated with the difference in carbon used by grazing versus cutting, indicating that cut grasslands have a greater on-site sink activity than grazed grasslands. However, the net biome productivity was significantly correlated to the total C used by grazing and cutting, indicating that, on average, net carbon storage declines with herbage utilisation for herbivores