为了研究氮沉降对内蒙古额尔古纳草甸草原主要温室气体(CO₂、CH₄和N₂O)排放通量的影响, 该研究通过添加NH₄NO₃模拟氮沉降, 并设置6个氮添加水平(0、2、5、10、20、50 g·m^-2·a^-1), 同时考虑到草地利用方式的影响, 设置刈割和不刈割2个处理水平。分别于2020年和2021年的生长季(5-9月), 采用静态箱-气相色谱法测定了3种温室气体的排放通量。主要结果有: 1)生长季内3种温室气体的排放通量对氮添加的响应呈明显的非线性, 但响应格局在3种温室气体之间存在明显的差异。2)当氮添加量达到5-10 g·m^-2·a^-1时, CO₂的通量达到峰值, 表现出显著的饱和性特征; CH₄的吸收在低氮添加(0-5 g·m^-2·a^-1)时受到促进, 且这种促进作用随着氮添加量的增加而增强, 但氮添加量达到5-10 g·m^-2·a^-1时, 对CH₄吸收的促进作用逐渐减弱, 且高氮添加(50 g·m^-2·a^-1)显著抑制CH₄的吸收; N₂O的排放通量对氮添加的响应总体也随氮添加量的增加而显著增加, 但响应模式与幅度存在年际差异。3)刈割仅在2021年对CH₄的吸收具有显著的促进作用。4)综合两年的结果, CO₂排放通量与降水量和硝态氮含量显著正相关, 与pH显著负相关。CH₄吸收通量与降水量和铵态氮含量显著正相关, 与pH显著负相关。N₂O排放通量与土壤温度和铵态氮含量显著正相关, 与硝态氮含量显著负相关。上述研究结果表明, 大气氮沉降增加对温室气体排放的影响具有普遍的非线性特征, 但不同温室气体的通量格局存在一定的差异。该研究结果对控制氮肥用量、选择合适的草地利用方式、评估草地生态系统变暖潜势具有重要意义。

Aims How nitrogen (N) addition impacts the emission of greenhouse gases (GHGs) is now becoming a hot issue in the study of global change. We aim to delineate the effects of N addition on the emission of major greenhouse gases (CO₂, CH₄and N₂O).

Methods In order to achieve this goal, the flux of the three major GHGs was measured using static chamber gas chromatography during the growing seasons (May through September) of 2020 and 2021 in a meadow steppe of Hulun Buir in Nei Mongol. The experiment was conducted by applying NH₄NO₃ to simulate the atmospheric N deposition, which involved six N addition levels (i.e., 0, 2, 5, 10, 20, 50 g·m^-2·a^-1) and two grassland utilization levels (i.e., mown and unmown).

Important findings The results showed that the response of the three GHGs to N addition showed clear nonlinear patterns, but there was a remarkable difference in the patterns among the three GHGs. The emission of CO₂ was increased with increasing N addition but saturated at around 10 g·m^-2·a^-1. The uptake of CH₄ was promoted with increasing N addition when N addition was low (0-5 g·m^-2·a^-1), but this promotion effect was diminished with further increase in N addition (5-10 g·m^-2·a^-1), and the uptake of CH₄ was inhibited when N addition reached 50 g·m^-2·a^-1. The emission of N₂O increased significantly with the increase of N addition rates, but the response patterns and amplitude showed remarkable difference between the two years. With the data in the two years pooled, the CO₂ flux had a significant positive correlation with precipitation and nitrate nitrogen (NO- 3-N) content, and a significant negative correlation with pH; CH₄ absorption flux was significantly positively correlated with precipitation and ammonium nitrogen (NH+ 4-N) content, while negatively correlated with pH; N₂O flux was significantly positively correlated with soil temperature and NH+ 4-N content, while significantly negatively correlated with NO- 3-N content. Our findings demonstrated that the response of the three GHGs to increasing atmospheric N deposition was largely nonlinear, and the response patterns were remarkably different among the three GHGs. These findings may be of great importance for controlling N fertilizer use, selecting appropriate grassland use, and evaluating grassland ecosystem warming potential under increasing atmospheric N deposition.