Belowground links between root properties of grassland species and N2O concentration across the topsoil profile.

Plants can affect N 2 O emissions by enhancing nitrogen (N) uptake and other below-ground interactions. However, the specific effect of the root systems of different plant species on the production and accumulation of N 2 O within the soil profile remain largely unknown. The aim of this study was to investigate how plant species from different functional groups, their productivity and root traits affect N 2 O emissions and N 2 O concentrations within the soil profile in a fertilised grassland. We conducted a field experiment with two grasses (Phleum pratense , Lolium perenne), two legumes (Trifolium repens , Trifolium pratense), two forbs (Cichorium intybus , Plantago lanceolata), and the six-species mixture in a fertilised grassland. The effects of these plant communities on N-cycling processes were then assessed through the measurement of above- and below-ground plant traits, plant productivity, soil nutrient availability, N 2 O emissions and its distribution in the soil profile. We found that C. intybus and P. pratense had the lowest N 2 O emissions from the soil, which was mainly related to higher root biomass. The six-species mixture also showed lower N 2 O emissions compared to L. perenne monoculture which was explained by complementary effects between the different plant species. We did not find a relationship between N 2 O emission and its concentration in the soil profile. Higher specific root length and root length density coincided with higher N 2 O concentrations at 10–20 and 20–30 cm soil depths. Since these two traits have been previously linked to reductions in N 2 O emissions emitted from the soil, our results show that the relationships between root traits and N 2 O emissions may not be reflected down in the soil profile. Overall, this study underscores the often-neglected importance of root traits for N-cycling and emphasises the need to better understand how root traits modify N 2 O consumption within the soil profile to design more sustainable grasslands. • C. intybus and P. pratense decreased N 2 O emissions due to higher root biomass. • Mixture lower N 2 O emissions compared to L. perenne due to complementary effects. • There is no relationship between N 2 O emission and its concentration in the soil profile. • Higher root traits coincided with higher N 2 O concentrations in the soil profile. [ABSTRACT FROM AUTHOR]