放牧强度对内蒙古半干旱草原地气间能量和物质交换的影响

利用涡度相关技术, 于2006年7月27日至8月10日在内蒙古半干旱草原三种放牧强度的下垫面进行微气象观测。本文分析了放牧强度对内蒙古半干旱草原地气间能量和物质交换的影响, 发现: (1)放牧降低植被覆盖率, 使地表反射率增大。(2)放牧使潜热通量减小。而放牧强度最大的锡林河河道潜热通量最大,表明土壤水分状况是半干旱草原地表能量收支的决定性因素。(3)羊草和冬季放牧观测点日平均CO2通量分别为-1.92 g?m-2?d-1和0.73 g?m-2?d-1, 表明放牧可以使草地由CO2的汇转变为源。锡林河河道为CO2的汇, 日平均CO2通量-3.35 g?m-2?d-1, 与羊草比较, 锡林河河道吸收CO2更多, 表明土壤湿度是影响半干旱草原CO2通量交换的重要因素。(4) 放牧通过减小叶面积指数, 减弱植被的光合作用能力。

Influence of Grazing Intensity on Energy and Mass Exchange between the Surface and Atmosphere over Semi-Arid Grassland in Inner Mongolia

Eddy eovariance technique was used m conduct the micrometeorological measurements over three kinds of semi-arid grasslands under three different grazing intensities in Inner Mongolia from 27 July to 10 August 2006. The influence of grazing intensities on the energy and mass exchange between the surface and atmosphere over semi-arid grasslands in Inner Mongolia was analyzed. The main results are listed as following: (1) Grazing reduced the vegetation cover ratio and therefore increased albedo. (2) Grazing decreased the latent heat flux. Although the Xilin River site had the pronounced grazing intensity, its latent heat flux was largest. This indicated that soil water condition was the key factor which controlled the sur-face energy budget over semi-arid grasslands.(3) The daily average CO_2 fluxes at Leymus site and winter grazed site were-1. 92 g·m~(-2)·d~(-1) and 0. 73 g·m~(-2)·d~(-1) respectively, which showed that grazing could make grasslands change from CO_2 sink to CO_2 source. The Xilin River site was CO_2 sink and its daily average CO_2 flux was-3. 35 g·m~(-2)·d~(-1). Compared to Leymus site, the Xilin River site absorbed more CO_2, indicating that soil moisture was an important factor which influenced CO_2 flux exchange over the semi-arid grassland.(4) By decreasing the leaf area index, grazing decreased the photosynthesis capacity of vegetations.