Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind speed variations. The transient response of sap flow was described using the resistance–capacitance model. The steady sap flow rate increased as the wind speed increased at low wind speeds. Once the wind speed exceeded 8.0 m s−1, the steady sap flow rate did not increase further. The transpiration rate, measured gravimetrically, showed a similar trend. The response of nocturnal sap flow to wind speed variation was also measured and compared with the results in the daytime. Under the same wind speed, the steady sap flow rate was smaller than that in the daytime, indicating differences between diurnal and nocturnal hydraulic function, and incomplete stomatal closure at night. In addition, it was found that the temporal response of the Granier sensor is fast enough to resolve the transient behaviour of water flux in plant tissue.
展开▼
机译：在风洞中通过实验研究了液流对风速阶跃变化的瞬态响应。在圆柱管中对Granier型液流传感器进行校准和测试，以分析其瞬态时间响应。然后，该传感器用于测量水分充足的帕奇拉（Pachira macrocarpa）植物对风速变化的瞬态响应。使用电阻电容模型描述了液流的瞬态响应。在低风速下，稳定的树液流量随风速的增加而增加。一旦风速超过8.0 m s -1 ，稳定的树液流量就不会进一步增加。用重量法测量的蒸腾速率显示出相似的趋势。还测量了夜间树液流量对风速变化的响应，并将其与白天的结果进行了比较。在相同的风速下，稳定的树液流量小于白天，表明昼夜液压功能存在差异，夜间气孔关闭不完全。另外，发现格兰尼尔传感器的时间响应足够快以解决植物组织中水通量的瞬态行为。
展开▼
