Abstract Nocturnal sap flow is an important part of plant sap flow, while it is usually regarded as negligible. Consequently, the aim of this study was to measure nocturnal stem sap flow of Acer truncatum and to determine its driving force in an urban green space. Stomatal aperture was measured using surface impression method in a typical clear day of August. Sap flux density was monitored by a thermal diffusive probe system from July to October. Meanwhile, wind speed (WS), relative humidity, air temperature, precipitation and total solar radiation were monitored by an automatic weather station. We found nocturnal stomatal aperture was about 32% of mid-morning, and nocturnal sap flux density was significantly and positively affected by WS and vapor pressure deficit (VPD) (P

中文翻译：

---

城市环境中的槭树夜间汁液流动主要是由于茎的再充盈而不是夜间蒸腾作用引起的

摘要 夜间树液流是植物树液流的重要组成部分，但通常被认为可以忽略不计。因此，本研究的目的是测量 Acer truncatum 的夜间茎液流并确定其在城市绿地中的驱动力。气孔孔径是在八月一个典型的晴天使用表面印迹法测量的。从 7 月到 10 月，通过热扩散探针系统监测树液通量密度。同时，自动气象站监测风速（WS）、相对湿度、气温、降水和总太阳辐射。我们发现夜间气孔孔径约为上午的 32%，夜间树液通量密度受 WS 和蒸气压不足（VPD）的显着影响（P