The pressure chamber, the most popular method used to measure xylem water potential, is a discontinuous and destructive technique and is therefore not suitable for automated monitoring. Continuous non-destructive monitoring could until very recently be achieved only by use of the thermocouple psychrometer (TP). Here we present the high-capacity tensiometer (HCT) as an alternative method for continuous non-destructive monitoring. This provided us with a unique chance to cross-validate the two instruments by installing them simultaneously on the same sapling stem. The HCT and the TP showed excellent agreement for xylem water potential less than –0.5 MPa. Response to day/night cycles and watering was remarkably in phase, indicating excellent response time of both instruments despite substantially different working principles. For xylem water potential greater than –0.5 MPa, the discrepancies sometimes observed between the HCT and TP were mainly attributed to the kaolin paste used to establish contact between the xylem and the HCT, which becomes hydraulically poorly conductive in this range of water potential once dried beyond its air-entry value and subsequently re-wetted. Notwithstanding this limitation, which can be overcome by selecting a clay paste with higher air-entry value, the HCT has been shown to represent a valid alternative to the TP.

中文翻译：

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用于连续监测树苗木质部水势的大容量张力计和热电偶干湿计的交叉验证

压力室是用于测量木质部水势的最常用方法，是一种不连续且具有破坏性的技术，因此不适合自动监测。直到最近，只能通过使用热电偶干湿表 (TP) 才能实现连续无损监测。在这里，我们提出了大容量张力计 (HCT) 作为连续无损监测的替代方法。这为我们提供了一个独特的机会来交叉验证这两种仪器，方法是将它们同时安装在同一个树苗茎上。HCT 和 TP 对低于 –0.5 MPa 的木质部水势表现出极好的一致性。对昼夜循环和浇水的响应显着同相，表明尽管工作原理大不相同，两种仪器的响应时间都非常出色。对于大于 –0.5 MPa 的木质部水势，有时在 HCT 和 TP 之间观察到的差异主要归因于用于在木质部和 HCT 之间建立接触的高岭土浆料，一旦干燥，高岭土浆料在该水势范围内的水力传导性较差超出其空气进入值并随后重新润湿。尽管可以通过选择具有较高进气值的粘土糊来克服这一限制，但 HCT 已被证明是 TP 的有效替代品。