Inoculation with nitrous oxide (N2O)-reducing denitrifier strains simultaneously mitigates N2O emission from pasture soil and promotes growth of pasture plants

Abstract The aim of this study was to screen nitrous oxide (N 2 O)-reducing denitrifier strains showing both N 2 O mitigation and plant growth-promoting (PGP) effects in soil systems, and the effects of selected strains were monitored in soil and plant, analyzed, and comparatively evaluated. Forty denitrifier strains affiliated with Azospirillum and Herbaspirillum, previously isolated from three different paddy soils, were evaluated. Of these, 11 produced indole-3-acetic acid(>5 μg mL −1 ), 9 promoted the growth of red clover( Trifolium pratense L. var. Medium) or timothy ( Phleumpratense L. var. Horizon) on agar plates, and 7 were inoculatedinto two different soils for cultivating red cloverand timothy in a greenhouse. Compared with non- inoculatedcontrol, N 2 O flux from red cloversoil and from timothy soil were significantly lower 8 and 14 days and 9 days onwards, respectively, after inoculationwith these seven strains. Cumulative N 2 O emissions from red cloversoil were significantly lowered through inoculationwith these seven strains. The growth parameters, including plant height, leaf area, fresh weight or dry weight, of the two pasture plants were significantly greater in soils inoculatedwith most of these seven strains than in non- inoculatedsoils. The uptake of C and N by the two pasture plants was significantly greater in soils inoculatedwith most of these seven strains than in non- inoculatedsoils. In conclusion, inoculatingN 2 O-reducing denitrifiers to pasture soil could mitigate N 2 O emissions and simultaneously promote the growth of pasture plants in a greenhouse. These strains will be invaluable microbiological resources for developing novel biofertilizers.