Effects of inorganic nitrogen and phosphorus enrichment on the emission of N₂O from a freshwater marsh soil in Northeast China

The freshwater marshes in northern China are heavily impacted by anthropogenic disturbances such as cultivation and fertilization and increased levels of nutrients (especially N and P) through atmospheric deposition and agricultural surface runoff. These disturbances have affected the emission of N₂O from these systems. This laboratory study was conducted to determine the effects of increased inputs of inorganic N and P on N₂O emission from marsh soil in response to different soil moisture conditions. The results showed that the emission of N₂O increased with the enhancement of N inputs when the soil was submerged, but that the highest N treatment suppressed the emission of N₂O when the soil was at 60% water holding capacity (WHC), which may have occurred due to an inadequate amount of available C. Furthermore, the results of this study indicated that a small amount of N fertilizer induced much more N₂O evolution from freshwater wetland soil, while P fertilizer inputs appeared to stimulate the emission of N₂O only during the first few days of the experiment. Additionally, soil that was treated with P appeared to absorb N₂O when it was at 60% WHC after around 6 weeks of the incubation, which indicates that the input of P fertilizer might serve as a shift of source or N₂O sink in wetland soils under non-flooded conditions. When compared to soil at 60% WHC, submerged soil had significantly higher N₂O emissions, except when subjected to the medial N treatment. These findings indicate that the soil moisture condition had a significant effect on N₂O emissions when the same amount of N or P was applied. Therefore, the effects of N and P fertilization in the northern temperate wetlands cannot be neglected from regional or national emissions of N₂O.