Greenhouse gas fluxes over managed grasslands in Central Europe.

Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site-specific management strategies strongly affect the biosphere-atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO ), nitrous oxide (N O), and methane (CH ). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO exchange, while long-term N O and CH flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO , N O, and CH fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO sink (-1,783 to -91 g CO  m  year ), but a N O source (18-638 g CO -eq. m  year ), and either a CH sink or source (-9 to 488 g CO -eq. m  year ). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between -2,761 and -58 g CO -eq. m  year , with N O and CH emissions offsetting concurrent CO uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N O and CH fluxes was generally low and varied considerably within years. However, after site-specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity ("sweet spots") and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N O and CH emissions. The N O-N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%-8.6%). Although grassland management led to increased N O and CH emissions, the CO sink strength was generally the most dominant component of the annual GHG budget.