夏季放牧强度对藏北草原温室气体排放的影响

高寒草原是我国青藏高原最主要的放牧草地类型之一,为了研究放牧强度对其温室气体排放的影响,在藏北紫花针茅(Stipa purpurea)草原进行不同放牧强度试验,并采用静态箱法在夏季放牧期间对不同放牧强度下CO2、CH4和N2O 3种主要的温室气体排放情况进行了测定。结果表明,高寒紫花针茅草原CO2的排放在适宜的放牧强度下随放牧强度的增加而增加,但当放牧强度继续增大至重牧水平时,CO2排放降低;放牧强度的增加会显著(P0.05)降低高寒紫花针茅草原对CH4的吸收,但不改变草原作为CH4汇的功能;轻牧对高寒紫花针茅草原N2O排放无显著影响,当放牧强度达中牧或重牧水平,N2O的排放也显著(P0.05)增加,且中牧与重牧相互之间差异显著(P0.05);以全球增温潜势折算总温室气体排放,CO2排放平均占总温室气体排放的约98%,CH4吸收和N2O的排放各只占约1%,CH4吸收与N2O的排放与放牧强度互为消长。

Effect of summer grazing intensity on GHG emission in the North Tibet steppe

A grazing intensity experiment was conducted to investigate the effect of summer grazing intensity on GHG emission in the North Tibet steppe dominated by Stipa purpurea through measuring CO2, CH4 and N2O emission with static chamber method. This study indicated that CO2 emission from the S.purpurea steppe increased with the increase of grazing intensity when the grazing intensity was moderate, and it decreased when the grazing density was heavy grazing density. The increase of grazing intensity significantly decreased the absorption of S.purpurea steppe for CH4 (P<0.05), but it did not affect the steppe function as a sink of CH4. Lightly grazing intensity had no significant effect on N2O emission of the S.purpurea steppe. However, N2O emission significantly increased when the grazing density was over middle grazing density (P<0.05). In this study, the global warming potential (GWP) was used to estimate the total GHG emissions of alpine steppe, the CO2 emissions accounted for nearly 98% of the total emissions, and the CH4 absorption and N2O emission only accounted for 1%, respectively, and their amount was trade off.