放牧对温带典型草原含碳温室气体CO_2、CH_4通量特征的影响

Effects of Grazing on Carbon Dioxide and Methane Fluxes in Typical Temperate Grassland in Inner Mongolia, China

利用静态暗箱法于2001年～2003年对内蒙古羊草和大针茅围栏禁牧草原及其放牧草原主要含碳温室气体CO2、CH4通量进行了野外连续定位试验研究,结果表明:与对照围栏禁牧草原相比,自由放牧和轮牧均没有改变土壤与大气间原有的CO2、CH4气体通量的源汇方向,也没有改变土壤通量的季节变化形式;2001年～2003年不同统计时段羊草围栏禁牧草原土壤平均CO2通量比羊草轮牧草原高9 6%～67 7%,大针茅围栏禁牧草原也比对应自由放牧草原CO2通量高约22 7%～59 4%,而在植物非生长季,自由放牧草原(或轮牧草原)土壤呼吸同对应的围栏禁牧草原相差不大;大针茅自由放牧草原和羊草轮牧草原土壤对CH4的年平均吸收通量均低于对应的围栏禁牧草原,放牧减弱了草原土壤对CH4的氧化吸收作用,但羊草轮牧和大针茅自由放牧草原与对应围栏禁牧草地土壤CH4平均通量的差异均未达到0 05的显著性水平,研究时段的干旱气候弱化了放牧草原与围栏禁牧草原间的差异;在植物生长季,放牧促进了土壤对CH4的氧化吸收,而在非生长季的部分时段尤其是春季冻融期又加大了CH4的正排放,放牧增加了土壤CH4通量的年变幅。

Using the static chamber method, the fluxes of carbon dioxide and methane of soil were measured through the continuous experiment in situ from July 2001 to July 2003 in Aneurolepidium Chinense and Stipa grandis fence-enclosed non-grazing grasslands and their corresponding grazing pastures in Xinlin river basin of Inner Mongolia in China. According to the results of field experiment, the fluxes characteristics and seasonal variation patterns of two non-grazing grasslands and their grazing grasslands were compared. The results indicated that: 1) Comparing with the native fence-enclosed communities, the grazing didn't changed the direction of sources and sinks and the seasonal variation patterns of the carbon dioxide and methane fluxes; 2) The average emission fluxes of carbon dioxide at different statistical period from 2001 to 2003 in Aneurolepidium Chinense fence-enclosed grassland were 9.6 percent to 67.7 percent higher than that of Aneurolepidium Chinense rotational grazing grassland and 22.7 percent to 59.4 percent higher in Stipa grandis fence-enclosed grassland than that in the Stipa grandis free-grazing grassland. While in non-growing season, the differences between fence-enclosed grasslands and corresponding rotational or free grazing grasslands weren't significant; 3) The annual CH_4 uptake fluxes of grazing grasslands were lower than those in corresponding fence-enclosed grasslands, the grazing decreased the soil sink intensity of CH_4. But the difference of annual or growing-season average CH_4 fluxes between fence-enclosed and grazing grasslands didn't reached the significance level of 0.05. The drought has narrowed the difference between them; 4) The grazing promoted the CH_4 uptake intensity of soil in growing season, while also promoted the emission fluxes of CH_4 in certain period of non-growing season especially during the period of freezing-thawing, the grazing enlarged the annual variation range of CH_4 fluxes.