Beneficial effects of multi-species mixtures on N₂O emissions from intensively managed grassland swards

In a field experiment, annual nitrous oxide (N₂O) emissions and grassland yield were measured across different plant communities, comprising systematically varying combinations of monocultures and mixtures of three functional groups (FG): grasses (Lolium perenne, Phleum pratense), legumes (Trifolium pratense, Trifolium repens) and herbs (Cichorium intybus, Plantago lanceolata). Plots received 150 kg ha^-1 year^-1 nitrogen (N) (150 N), except L. perenne monocultures which received two N levels: 150 N and 300 N. The effect of plant diversity on N₂O emissions was derived from linear combinations of species performances' in monoculture (species identity) and not from strong interactions between species in mixtures. Increasing from 150 N to 300 N in L. perenne resulted in a highly significant increase in cumulative N₂O emissions from 1.39 to 3.18 kg N₂O-N ha^-1 year^-1. Higher N₂O emissions were also associated with the legume FG. Emissions intensities (yield-scaled N₂O emissions) from multi-species mixture communities around the equi-proportional mixture were lowered due to interactions among species. For N₂O emissions scaled by nitrogen yield in forage, the 6-species mixture was significantly lower than L. perenne at both 300 N and 150 N. In comparison to 300 N L. perenne, the same N yield or DM yield could have been produced with the equi-proportional 6-species mixture (150 N) while reducing N₂O losses by 63% and 58% respectively. Compared to 150 N L. perenne, the same N yield or DM yield could have been produced with the 6-species mixture while reducing N₂O losses by 41% and 24% respectively. Overall, this study found that multi-species grasslands can potentially reduce both N₂O emissions and emissions intensities, contributing to the sustainability of grassland production.