城市与区域生态国家重点实验室知识库

      随着城市化进程的加速，城区环境相比于郊区发生了极大地改变，进而影响
了城市植物的正常生长和水分代谢过程。因此，研究城区和郊区环境下植物水分
利用特征及影响机制对水资源管理具有重要意义。本研究利用热扩散技术和自动
气象站对北京教学植物园（油松、雪松、刺槐）和蟒山（油松）树干液流及其影
响因子进行连续同步监测，主要研究结果如下：
（1）在不同时间尺度下教学植物园大气温度和水汽压亏缺均高于蟒山，空气相对湿度和太阳总辐射整体上表现为植物园低于蟒山，但蟒山地区风速显著大于教学植物园。教学植物园内氮氧化物（NO 和NO2）浓度和颗粒物（PM2.5）浓度明显高于蟒山地区，臭氧浓度低于蟒山地区。
（2）油松北面和南面树干液流密度的日变化均呈单峰格局，且南向树干液流密度均略高于北向，但差值不大。雪松树干液流各个方位的日变化在春秋季节均呈单峰曲线，在夏季出现双峰曲线，雪松南北向树干液流大于东西向。刺槐树干液流各个方位的日变化均呈单峰曲线，不同季节各个方位的液流大小表现不同。
（3）城区三个树种生长季树干液流密度日均值表现为油松 > 刺槐 > 雪松，但蒸腾年累积量表现为雪松 > 油松 > 刺槐。油松和刺槐两树种树干日液流密度均呈单峰曲线；雪松树干日液流密度夏季出现“午休”现象，呈双峰曲线，春秋季节呈单峰曲线。
（4）城区油松、雪松和刺槐树干液流密度的月变化规律明显，7-8 月份达到峰值，12 月、1 月和2 月最低，油松和雪松树干液流密度3 月份以后开始迅速上升，而刺槐液流密度4 月份以后才开始迅速上升。由于植物自身物候期以及对环
境变化敏感度的差异，研究树种树干液流的年内差别比较大。蟒山油松树干液流
密度在生长季出现明显低谷，可能与6 月降雨频次和降雨量增加有关。在年尺度
上，油松、雪松和刺槐年平均液流密度、日蒸腾量和年累积蒸腾量各年份间均无
显著差异（P > 0.05）。
（5）不同年份影响树干液流密度的主要环境因子存在差异。水汽压亏缺、太阳总辐射、大气温度和土壤温度是影响教学植物园油松和雪松树干液流密度的主要环境因子；土壤温度是影响教学植物园刺槐树干液流密度的主要环境因子。太阳总辐射、大气温度和水汽压亏缺是影响蟒山油松树干液流的主要环境因子。
（6）教学植物园油松树干液流密度显著高于蟒山油松（P < 0.05）。这主要与城区大气温度增加，空气相对湿度降低，水汽压亏缺增大有关。城区环境因子变化促进了植物蒸腾耗水，最终导致城区环境下油松树干液流密度高于郊区。
      总之，城区和郊区环境下植物水分利用存在较大差异。研究结果对准确地衡量北京城区和郊区树木的水分利用特征十分关键，对协调城区绿地发展和山区植
被建设及水资源利用和管理具有重要的科学意义，同时可以为城市树木生态功能
和服务的评估提供有用的数据支撑。

      The urban environment has changed greatly compared with that of the suburbs, which further affects the normal growth and water metabolism of urban plants. Therefore, studying the characteristics and impact mechanism of plant water use in urban and suburban environments is of great significance for water resource management. This study continuously monitor the sap flow of typical greening species of Beijing Teaching Botanical Garden (Pinus tabulaeformis, Cedrus deodara, Robinia pseudoacacia) and Mangshan (Pinus tabulaeformis) and its influencing factors using thermal diffusion technology and automatic weather station. The main findings were as follows:
(1) Compared to Mangshan, it was found that the atmospheric temperature (Ta) and water vapor pressure deficit (VPD) were higher, the air relative humidity (RH) and total solar radiation (Rs) were lower, and wind speed was significantly lower in Beijing Teaching Botanical Garden. Compared to Mangshan, the concentration of nitrogen oxides and particulate matter in Beijing Teaching Botanical Garden were significantly higher, but the concentration of ozone was lower.
(2) The diurnal variation of sap flow density of Pinus tabulaeformis (pine) in the north and south direction both showed a single peak pattern, with the southward slightly higher than that in the northward. The diurnal variation of Cedrus deodara (cedar) sap flow density in each direction all shows a single-peak curve in spring and autumn and a double-peak curve in summer, with the north-south direction larger than the east-west direction. The diurnal variation of Robinia pseudoacacia (locust) sap
flow density in each direction all showed a single-peak curve, and the size was different in different seasons.
(3) The average daily sap flow density under urban environment in the growing season was presented as pine > locust > cedar, but the annual accumulation of transpiration was presented as cedar > pine > locust. The daily sap flow density of pine and locust showed a single-peak curve, while that of cedar showed a double-peak curve in summer and a single-peak curve in spring and autumn.

 (4) The monthly average sap flow density amounted to the peak level in July and August, while declined to the lowest level in December, January and February in Beijing Teaching Botanical Garden. The sap flow density of pine and cedar began torise rapidly after March while that of locust began to rise rapidly after April. In the growing season, the sap flow density of pine in Mangshan showed a significant trough, which may be related to the increase of rainfall frequency and amount in June. There
was insignificant difference in annual mean sap flow density, daily transpiration and annual transpiration of three tree species between different years in Beijing Teaching Botanical Garden.
(5) The main environmental factors influencing the sap flow in different research years were different. In Beijing Teaching Botanical Garden, VPD, Rs, Ta and soil temperature (Ts) are the main environmental factors affecting the sap flow of pine and cedar. And Ts is the main factor affecting the sap flow of locust. In Mangshan, Rs, Ta and VPD are the main factors affecting the sap flow of pine.
(6) The sap flow density of pine in Beijing Teaching Botanical Garden was
significantly higher than that in Mangshan. This was mainly related to the increase of Ta and VPD, and the decrease of RH in urban environment. The change of these environmental factors in the urban could promote the transpiration of plants.
Eventually, the sap flow of the pine in the urban was higher than that in the suburban environment. The research results are critical to accurately measure the water use characteristics of trees in urban and suburban areas, and have important scientific significance for the coordinated development of urban green space and mountain vegetation construction, and water resources management.