南京近郊麻栎林冠层蒸腾时间变化及降温效应

Temporal variation for canopy transpiration and its cooling properties in a Quercus acutissima forest of suburban Nanjing

2012年9月和10月及2013年5-8月,利用树干液流仪和小气象站对南京近郊东善桥林场的麻栎Quercus acutissima树干液流速率及环境因子进行连续观测,分析麻栎林冠层蒸腾量及其对周边环境的降温效应。结果表明:1各月麻栎液流密度均在13:00左右达到最大值,其中8月峰值最高(18.78 g·cm-2·h-1),6月峰值最低(13.49 g·cm-2·h-1);25-10月麻栎林冠层蒸腾总量为237.52 mm,7月冠层蒸腾量最高(50.46 mm),10月冠层蒸腾量最低(29.86mm);37月的蒸腾耗能量与太阳辐射能量值最高,分别为154.97 MJ·m-2,489.65 MJ·m-2,8月冠层蒸腾耗能系数最高(35.82%),10月的冠层蒸腾耗能系数最低(25.76%);4麻栎林7月冠层蒸腾降温值最高(3.07℃),生长期平均可降温(2.35±0.53)℃。

Global warming and regional water resources shortage have become the focus of the global. Climate warming affects global hydrological cycles, and tree transpiration also affects climate warming. This study was conducted to analyze canopy transpiration of Quercus acutissima and to determine its cooling effect on sur- rounding environments. Continuous observation of the sap flow density and environmental factors, such as solar radiation, air temperature, air relative humidity, soil temperature, soil water content, used a sap flow meter and a mini weather station in Nanjing Dongshanqiao Forest Farm. Maximum sap flux density, peak daily sap flux density, transpiration heat flux, solar energy, consumed-energy coefficient, and canopy transpiration cooling was conducted according these data. Six trees of different diameter grade were observed. Results indicated that 1 ） the maximum sap flux density appeared at 13：00; the greatest peak daily sap flux density was 18.78 g-cm-2.h-1 in August, and the lowest was 13.49 g.cm-2.h-1 in June. 2） Canopy transpiration summed from May to October was 237.52 mm with the highest month being July. 3） July also had the greatest transpiration heat flux （154.97 MJ. m-2） and solar energy （489.65 MJ·m^-2）. The coefficient of consumed-energy for canopy transpira- tion was highest in August （35.8%） and lowest in October （25.8%）. 4） Canopy transpiration cooling from Q. acutissima was highest in July （3.07℃）, and during the growing season, canopy transpiration reduced the average temperature （2.35±0.53）℃·h^-1 per 10 m^3 air. According to the transpiration and its cooling effect, we could choose suitable afforestation design in order to alleviate global warming and heat island effect