Forest Fine Root Litter Mitigates the NH3 Volatilization and N2O Emission from N-Applied Agriculture Soil

Forest fine root litter enters agricultural soils in some cases and its decomposition would change the soil's properties. However, how this process further influences the ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission from agricultural soil receiving fertilizer nitrogen (N) is unknown. Here, we conducted a soil pot experiment to investigate the responses of the aforementioned gaseous N losses during wheat season to fine root litters derived from <i>Populus deltoides</i> (RP) and <i>Metasequoia glyptostroboides</i> (RM) incorporations. The results showed that two forest fine root litters reduced total NH₃ losses by 30.6-31.9% from 180 kg N ha^-1 applied to farmland soil, and this effect was attributed to decreased soil urease activity and ammonium-N during the basal N fertilization period. Whether receiving fertilizer N or not, N₂O emissions from farmland soil were significantly (<i>p</i> < 0.05) mitigated by 62.8-68.2% and 43.0-50.0% following the RP and RM incorporation, respectively. Lower N₂O emission was ascribed to increased soil pH but decreased soil nitrate-N and bulk density. In addition, less AOA and AOB <i>amoA</i> but more <i>nosZ</i> gene abundances explained the fine root litter-induced N₂O mitigation effect. Neither forest fine root litter exerted a negative effect on wheat grain yield and crop N use efficiency in N-added agriculture soil. In conclusion, forest fine root litter incorporation could help to mitigate gaseous N losses via NH₃ volatilization and N₂O emission from fertilizer-N-applied agricultural soils, and without crop production loss.