放牧对若尔盖高原湿地CH4排放的影响

湿地是大气甲烷(CH_4)的主要排放源,而有关放牧对湿地CH_4排放的影响特征仍未得到足够的报道。因此,通过静态箱法,研究了放牧对四川省若尔盖高原湿地CH_4排放的影响,CH_4气体通过快速温室气体分析仪测量。结果表明:放牧样地和围栏内样地生长季CH_4排放量为(31.32±19.57)g/m~2和(30.31±23.46)g/m~2,它们之间无差异显著;但是集中放牧期间(7—9月),放牧样地(21.01±12.35)g/m~2较围栏内样地显著增加了CH_4排放量为54.3%。2014年生长季期间通过刈割植物模拟放牧表明两种刈割强度CH_4排放量为(5.01±5.37)g/m~2和(4.69±5.99)g/m~2,较未刈割样地(1.15±1.89)g/m~2增加了335.9%和308.0%,其原因可能是放牧或者刈割减少地表植物生物量,降低植物高度,缩短了CH_4排放的路径距离。该结果可为我国高原湿地保护与管理决策提供基础数据支撑。

Effects of grazing on the emission of CH4 flux in the Zoige Plateau wetland

Wetland ecosystems, as the main source of atmospheric methane (CH₄), could seriously affect the concentration of atmospheric CH₄ and further climate change. Presently, wetland ecosystems have been severely affected by human actives (i.e., drainage, grazing, and harvesting). However, the effects of grazing on the CH₄ emission of wetland ecosystems have not been well investigated. Therefore, to evaluate the effects of grazing on the emission of CH₄ flux, we performed the field experiments in the Zoige Plateau wetland, southwestern China, from June to October 2013. We also performed field experiments to investigate the effects of simulated increased in sheep or yak grazing by the clipping on CH₄ emission in the same studied sites from May to October 2014. CH₄ emission was measured using a dark static chamber and the fast greenhouse gas analyzer (FGGA) during the two growing season. We observed an obvious seasonal variation in CH₄ emission at the studied sites. The CH₄ emission varied from -0.42 to 18.06 mg m^-2 h^-1 and its maximum value occurring in summer and/or autumn. These results showed that the CH₄ emission in the grazing and fencing plot was (31.32±19.57) g/m² and (30.31±23.46) g/m², respectively, during the growing season, and there were no significant differences in CH₄ emission between grazing and fencing plots (P > 0.05).However, the CH₄ emission in the grazing plot was (21.01±12.35) g/m² during heavy grazing periods (from July to September 2013), which was 54.3% higher than that in the fencing plot (un-grazed plot). Moreover, the results revealed that the CH₄ emission in the two clipping plots with 8 cm and 4 cm of vegetation height after clipping were (5.01±5.37) g/m² and (4.69±5.99) g/m², respectively, during the growing season, which were significantly higher in the 8 cm vegetation height in the clipping plot (335.9%) than that in the non-clipping plot (1.15±1.89) g/m² (P < 0.05), and 308.0% higher in the 4 cm vegetation height in the clipping plot than that in the non-clipping plot. Furthermore, we also measured the aboveground biomass in both the grazing and clipping plots. The results indicated that grazing decreased the aboveground biomass, which was 37.5% lower than the control plot ((525.88±103.47) g/m² vs. (886.09±124.46) g/m²) (P < 0.05). We also found a significantly negative correlation between aboveground biomass and CH₄ emission in August (P < 0.05), which may imply that CH₄ flux emissions decrease due to the reduced height of herbaceous vegetation. In summary, the results of the present study suggested that the sheep or yak grazing and clipping disturbance increased CH₄ emission in plateau wetland, via the reduction of the transporting distance from soil to the atmosphere due to significantly decreased aboveground biomass. This result provides the basic date for habitat protection and management in the plateau wetland in China.