绿洲不同覆被下环境CO_2浓度及小气候的变化

Variation in ambient CO_2 concentration and microclimate under different oasis land cover types

为了探讨局地CO2浓度时空变化特点和绿洲不同覆被的环境效应,在甘肃省河西走廊中段临泽绿洲北部,分别于春、夏、秋、冬季利用LI-6400便携式光合作用测定系统,研究了绿洲内樟子松林、杨树林、玉米地的环境CO2浓度和空气温度、湿度、光照强度等的变化,并与沙漠区进行了比较。结果表明,临泽绿洲北部近地层(≤10 m)大气CO2浓度年平均为372μmol.mol-1,夏季玉米叶片分布层1 m高处CO2浓度可降到320μmol.mol-1。绿洲区气温一年四季总体低于沙漠区,但不同植被类型效应不同,樟子松林和杨树林在夏季近地层气温低于沙漠区4.1℃,而玉米地则高于沙漠区2.3℃;空气相对湿度绿洲内明显高于沙漠区,年平均高出11.4%。说明绿洲森林植被具有明显的冷湿效应,特别是在夏季玉米农田气温高于沙漠的情况下,森林的冷效应更加明显。保护绿洲农田防护林网的完整和适宜的绿洲片林,具有维持绿洲冷湿效应的重要作用。

Variations in micro-environmental factors in Pinus sylvestris forest, Populus gansuensis var. mongolica forest and corn field in the spring, summer, autumn and winter seasons in the northern part of Linze Oasis, which is the middle section of Hexi Corridor,in Gansu Province, were studied. Atmospheric CO2 concentration was determined using LI-6400 portable photosynthetic system CO2 analyzer. Variations were compared with observed data from desert. The results show that mean annual atmospheric CO2 concentration of ground layer （≤ 10 m） in the northern part of Linze Oasis is 372 μmol·mol^-1 ; atmospheric CO2 concentration of ground layer under different vegetation types is lower than that for desert; and in the summer, CO2 concentration at l m height of leaf-distribution layer of corn decreases to 320 μmol·mol^-1. Air temperature for the four seasons is lower in the oasis than in deserrs. In the summer, air temperature in ground layer under P. sylvestris var. mongolica and P. gansuens/s forests is 4.1℃ lower than that of deserts,while in corn fields it is 2.3℃ higher than that of deserts. Annual air relative humidity of oases is significantly higher than that of deserts ; it surpasses that of deserts by 11.4% per annum. It is shown that forest oases have obvious cooling and wetting effects ,especially in the summer, when air temperature is higher on farmlands than in deserts, making the cooling and wetting effects of the forest even more pronounced. The presence of forest shelter for farmlands and patch forest oases plays a very significant role in maintaining cooling and wetting effects of oasis.