模拟氮沉降对内蒙古克氏针茅草原N2O排放的影响

随着工农业和社会的快速发展,我国成为全世界氮沉降最高的国家之一,温带草原地区的氮沉降水平局部可能超过3g·(m~2·a)~(-1).为研究氮沉降对我国典型草原生态系统氮循环的影响,在内蒙古太仆寺旗的克氏针茅草原,对土壤氧化亚氮(N_2O)的排放进行了为期1 a测定;同时,对该天然草地施加Na NO_3~-N以模拟氮沉降增加,进行了6个水平:CK(对照)、N_2[2g·(m~2·a)~(-1)]、N5[5 g·(m~2·a)~(-1)]、N10[10 g·(m~2·a)~(-1)]、N_25[25 g·(m~2·a)~(-1)]和N50[50 g·(m~2·a)~(-1)]的野外控制实验.结果表明,在自然氮沉降条件下,该生态系统N_2O的排放主要取决于土壤含水量和土壤温度,通过参数拟合估计全年N_2O-N排放量为0.10 g·(m~2·a)~(-1),约为当地氮沉降量的3%.而提高氮沉降可以显著提高N_2O的排放,特别是在高氮处理下(N_25和N50),N_2O的年排放量与模拟氮沉降量呈线性关系.我国温带典型草原较高的温室气体N_2O排放值得关注.

Effect of Stimulated N Deposition on N2O Emission from a Stipa krylovii Steppe in Inner Mongolia, China

With fast development of industry, agriculture and society, very high N deposition occurs in China. N deposition has exceeded 3 g· (m²·a)^-1 in some areas of temperate steppes, which is a significant part of the Eurasia grassland, but may possibly be sensitive to N deposition. To study the effect of N deposition on N cycling in typical temperate steppe, N₂O emissions were measured in a Stipa krylovii steppe in Inner Mongolia for a whole year. A field control experiment of simulated N deposition (by NaNO₃ addition) was also carried out at 6 dose levels, CK (control), N2 [2 g·(m²·a)^-1], N5 [5 g·(m²·a)^-1], N10 [10 g·(m²·a)^-1], N25 [25 g·(m²·a)^-1], and N50 [50 g·(m²·a)^-1]. The results showed that the natural N₂O-N emission flux was 0.10 g·(m²·a)^-1, accounting for about 3% of the total N deposition, and much depended on soil water content and soil temperature under ambient N deposition. In addition, enhanced N deposition might significantly increase N₂O emission, especially at very high N doses (N25 and N50 treatments). The annual N₂O emission flux showed a linear relationship with the N addition. Greater attention should therefore be paid to the relatively high N₂O emission in the typical temperate steppe in China.