中文摘要：

草地是城市绿地的重要组成部分，其对小气候环境的改善作用需定量评估。故于5月在北京使用涡度相关系统连续观测草地与裸地水热通量、CO2通量及其环境因素数值。结果表明晴天草地所获得的净辐射能量约1／2用于植被蒸腾和土壤蒸发，约13％用于显热；而裸地所获得的净辐射能量约1／3用于土壤蒸发，约2／5用于显热。中午草地温度比裸地温度最小低约10℃，比气温最大高约4℃。草地上水汽浓度比裸地最大高约3g／m^3，约高出1／3，具有增湿作用。在植被生长季节草地是CO2汇，是氧气的源，CO2通量日平均约-0．07mgm^-2·s^-1。草地发挥着降温增湿、释氧固碳、调节小气候等生态效应。

英文摘要：

Grassland is an important part of urban green space. In this study heat, .water, carbon dioxide fluxes and the environmental variables were measured continuously with the eddy covariance systems over grassland and bare soil in May in Beijing. The results indicated about half of net radiation energy was change to transpiration and about 13% to sensible heat over grassland on sunny day. However, about one third of net radiation energy change to evaporization and about two fifth to sensible heat over bare soil. The temperature of grassland was 10% lower than that of bare soil at noon, and is higher than that of atmosphere. The vapor concentration over grassland was 3 g/m^3 more than that over bare soil, with good moisfure effect. During the growing season, grassland is the sink of carbon dioxide and the source of oxygen. The diurnal average of carbon dioxide flux reaches about -0. 07 mg· m^-2 · s^-1. Grassland has ecological effects on decreasing temperature, enhancing moisture, and modifying microclimate in urdan areas.