The Responses of N₂O, CO₂ Emissions, and Bacterial Communities to Nitrogen Addition in Saline-Alkaline Wetlands of Northeast China

The Zhalong Wetland is impacted by elevated atmospheric nitrogen (N) deposition and N inputs from agricultural fertilization, which in turn affect greenhouse gas (GHG) emissions. It is unclear how N addition affects nitrous oxide (N2O) and carbon dioxide (CO2) emissions in this wetland. Therefore, we conducted a short-term experiment, collecting soil samples from three representative points with different water levels, and five N addition levels (N0 = 0 mg N kg(-1), N10 = 10 mg N kg(-1), N30 = 30 mg N kg(-1), N50 = 50 mg N kg(-1), N100 = 100 mg N kg(-1)) were used to simulate N input. Overall, N2O emissions were significantly increased by N addition. Differently, N addition had a significant suppressive effect on CO2 emissions in high-flooded soils, whereas the highest CO2 emissions were regarded under the N30 treatment in middle-flooded and dry soils. Through Pearson's correlation analysis, we found a significant positive correlation between N2O emissions and ammonium (NH4+), and CO2 emission was significantly positively correlated with pH and total organic carbon (TOC). Meanwhile, the bacterial community of the soil was analyzed via high-throughput sequencing. The results revealed that N addition was not significantly affecting soil bacterial community structure, while the three points were significantly different. Among them, the relative abundance of the dominant genera of Trichoderma and Pseudomonas were significantly enhanced after N addition. Furthermore, the bacterial communities were found to be significantly correlated with soil pH, TOC, NH4+, and nitrate contents, which affected N2O and CO2 emissions.