Long-term manure amendment reduces nitrous oxide emissions through decreasing the abundance ratio of amoA and nosZ genes in an Ultisol.

Organic fertilizers are frequently applied to soils to improve soil multifunctionality and maintain crop productivity in agricultural practices. However, how organic fertilizations influence soil nitrous oxide (N 2 O) emissions remains ambiguous, especially considering their linkage with the abundance of nitrogen (N)-cycling microorganisms. Here, we conducted an incubation experiment to examine the effect of partial replacement of mineral fertilizers with organic fertilizers on the abundance of N-cycling functional genes and N 2 O emissions at 60 % and 100 % water-filled pore space (WFPS) in an acidic Ultisol. Soil samples were collected from 32-year fertilization trials, including four treatments of control (no fertilizer), mineral NPK fertilizer (NPK), NPK + Peanut Straw (NPKS), and NPK + Pig Manure (NPKM). The N 2 O emissions from soils incubated at 100 % WFPS were significantly higher than those at 60 % WFPS in all treatments. Compared with NPK, NPKS and NPKM reduced N 2 O emissions, with a more pronounced effect in NPKM. The N 2 O flux was positively associated with the abundance of AOA and AOB amoA genes, and the abundance ratio of amoA / nosZ (i.e., the ratio of AOA amoA plus AOB amoA and nosZ І plus nosZ ІІ) when the peak N 2 O flux appeared. Random forest analysis showed that the abundance ratio of amoA / nosZ was the best predictor for N 2 O emissions. Compared with NPK, NPKM increased soil pH but reduced the abundance ratio of amoA / nosZ , which might be the key factor in reducing N 2 O emissions. Together, our findings suggested that long-term manure application reduced N 2 O emissions by decreasing the abundance ratio of amoA / nosZ and provided novel insights into the impact of organic fertilizers on N 2 O emissions in acidic agricultural soils. • N 2 O emissions are higher in soils incubated at 100 % WFPS than at 60 % WFPS. • Partial replacement of mineral fertilizers with pig manure reduces soil N 2 O emissions. • N 2 O emissions are positively associated with the abundance ratio of amoA / nosZ. • Manure application increases soil pH and reduces the abundance ratio of amoA / nosZ. [ABSTRACT FROM AUTHOR]