[Objective]Previous researches on the cooling and humidifying effects of urban green space mainly base on the large-scale and obscure the influence of plant community structure and tree species. However,this study based on the fine-scale investigated the daily dynamics in air temperature and relative humidity and the accurate cooling and humidifying effects of the five landscape plant communities during a calm sunny summer day,aiming to provide a reference for their landscape application as well as provide the theoretical basis for planning and construction of the urban green space system. [Method]In the Beijing Olympic Forest Park,five landscape plant communities with different canopy structure characteristics, including Populus tomentosa community, Ulmus pumila community, Salix matsudana community,Koelreuteria paniculata community,and Ginkgo biloba community,were selected as the research object. The open turfgrass lawn served as control open space site. The air temperature,relative humidity,wind speed,and canopy structure characteristics were measured in the field on calm sunny summer days. The collected data were processed and quantitatively analysed in every minute through the EXCEL2010 and SPSS19. 0 software,to detect the detailed diurnal variation in the air temperature and relative humidity of the every studied community and to compare the cooling and humidifying effects among the five communities. [Result]The results showed that diurnal variation in the air temperature and relative humidity of the five plant communities displayed a single peak in the 24 h of a day and the periods in which a state of high temperature and low humidity was maintained were different among the communities. The period of high temperature and low humidity appeared at 11:00 to 16:00 in P. tomentosa community,12:00 -17:00 in G. biloba community,and 11:00 to 17:00 in S. matsudana community which was relatively longer than other communities. However,there was no obvious high temperature and low humidity state in U. pumila and K. paniculata communities. Additionally,all the five plant communities had the significant cooling and humidifying effects during 08:00 to 18:00 when they lowered the air temperature by 3. 0 to 4. 3 ℃ with an average of 3. 7 ℃. Meanwhile,compared with the control open space site,they increased the relative humidity by an average of 11. 3% and ranged from 10. 2% to 12. 8%. However,these two effects in the studied communities were not significantly different from the control during 18:00 to 08:00 except in the U. pumila community. [Conclusion]On the basis of measured data per minute,there was a unimodal diurnal variation in these two microclimate indices in the five frequently-used communities and the diurnal variation in air temperature was more stable than that in relative humidity. Moreover,these plant communities had different influence on the air temperature and relative humidity within the internal environment likely because of the difference in canopy structure characteristics. These cooling and humidifying effects tended to be significant during the daytime while they were not significant during the night. Therefore,this study might form a theoretical reference for people to pleasantly employ the urban green space with the five tree species. Furthermore,other frequently-used tree species would be investigated on this issue,to provide a reference for the scientific planting design to build a urban green space with the pleasing temperature and humidity,as well as to promote the comfort degree for outdoor activities.%[目的]以往有关园材绿地降温增湿作用的研究主要基于大尺度,模糊了绿地中具体的群落结构和树种影响,本研究基于小尺度探讨5 种植物群落连续的温湿度日变化动态和准确的降温增湿作用,为其园林应用提供参考,也为城市绿地系统的规划和建设提供理论依据.[方法]于天气晴朗且无风的夏季,在北京奥林匹克森林公园选取毛白杨、榆、旱柳、栾树、银杏5 种冠层结构特征不同的植物群落作为研究对象,以空旷草坪为对照,分别对5种植物群落及对照点的空气温度、相对湿度、风速和冠层结构参数进行测试,以每分钟的数据为基础,利用EXCEL2010 和 SPSS19. 0 软件对测定结果进行数据处理和量化分析,研究了每种植物群落完整的温湿度日变化规律,比较不同植物群落之间降温增湿作用的差异.[结果]5 种植物群落的温湿度在24 h中均呈现出"单峰型"的变化规律,且各个群落在1 天中处于高温低湿状态的时间段各不相同,毛白杨群落是 11:00—16:00,银杏群落是12:00—17:00,旱柳群落的高温低湿时段最长,为 11:00—17:00,而榆树和栾树群落未出现明显的高温低湿时间段.此外,在08:00—18:00,5 种植物群落都具有明显的降温增湿作用,日均降温3. 0 ~4. 3 ℃,平均为3. 7 ℃; 日均增湿10. 2% ~12. 8%,平均为11. 3%;而在18:00—08:00,5 种植物群落与对照点之间的温湿度差异并不显著,仅榆树群落具有不明显的降温增湿作用.[结论]基于每分钟的测定数据,该研究展示了北京5 种常见植物群落在1天中的温湿度日变化趋势,且温度的日变化趋势比湿度更加稳定.同时,由于各个群落的冠层结构特征存在一定差异,因此不同植物群落对其内部环境温湿度表现出不同的调节作用,该作用在白天时段达到显著水平,而在夜间降温增湿作用并不明显.
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