Greenhouse gas fluxes over managed grasslands in Central Europe

Abstract 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 2 ), nitrous oxide (N 2 O), and methane ( CH 4 ). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO 2 exchange, while long‐term N 2 O and CH 4 flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO 2 , N 2 O, and CH 4 fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO 2 sink (−1,783 to −91 g CO 2 m −2 year −1 ), but a N 2 O source (18–638 g CO 2 ‐eq. m −2 year −1 ), and either a CH 4 sink or source (−9 to 488 g CO 2 ‐eq. m −2 year −1 ). The net GHG balance ( NGB ) of nine sites where measurements of all three GHG s were available was found between −2,761 and −58 g CO 2 ‐eq. m −2 year −1 , with N 2 O and CH 4 emissions offsetting concurrent CO 2 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 2 O and CH 4 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 2 O and CH 4 emissions. The N 2 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 2 O and CH 4 emissions, the CO 2 sink strength was generally the most dominant component of the annual GHG budget.