The stability enigma of hydraulic vulnerability curves: addressing the link between hydraulic conductivity and drought-induced embolism
The stability enigma of hydraulic vulnerability curves: addressing the link between hydraulic conductivity and drought-induced embolism
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DOI：
10.1093/treephys/tpz078
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发表时间：
2019-10-01
期刊：
影响因子：
4
通讯作者：
Steppe, Kathy
中科院分区：
文献类型：
--
作者：
De Baerdemaeker, Niels J. F.;Arachchige, Keerthika Nirmani Ranathunga;Steppe, Kathy
在干旱条件下维持木质部水分运输对植物至关重要，但当干旱诱导的栓塞形成并逐渐通过木质部扩散时，确实会发生木质部衰竭。水力方法被广泛认为是量化干旱引起的木质部栓塞的金标准。该方法确定水力传导率（K-h）在削减分支样品，脱水到特定的干旱水平，通过推动水通过他们。该技术因其可靠的K-h测量而被广泛认为，但在文献中关于如何定义稳定的K-h以及如何与木质部栓塞形成的程度相关存在一些不确定性。因此，该方法的最常见设置扩展为测量四个参数：（i）入口K-h，（ii）出口K-h，（iii）从木质部到周围活组织的径向流和（iv）样品两端的压差。从严格的理论观点来看，水力稳定状态，其中流入等于流出并且径向流为零，将导致稳定的K-h。设置在苹果上的应用。分支表明，达到水力稳定状态需要相当长的时间（高达300分钟），达到稳定状态的时间随着木质部水势的下降而增加。在每个实验运行期间，K-h和木质部水势动态增加，这是由X射线计算机微断层扫描可视化栓塞再填充下的高（8千帕）和低压（2千帕）头的支持。因此，供应加压水可能导致人工再填充血管，这使得难以在部分栓塞的木质部中实现真正稳定的K-h。
Maintaining xylem water transport under drought is vital for plants, but xylem failure does occur when drought-induced embolisms form and progressively spread through the xylem. The hydraulic method is widely considered the gold standard to quantify drought-induced xylem embolism. The method determines hydraulic conductivity (K-h) in cut branch samples, dehydrated to specific drought levels, by pushing water through them. The technique is widely considered for its reliable K-h measurements, but there is some uncertainty in the literature over how to define stable K-h and how that relates to the degree of xylem embolism formation. Therefore, the most common setup for this method was extended to measure four parameters: (i) inlet K-h, (ii) outlet K-h, (iii) radial flow from xylem to surrounding living tissue and (iv) the pressure difference across the sample. From a strictly theoretical viewpoint, hydraulic steady state, where inflow equals outflow and radial flow is zero, will result in stable K-h. Application of the setup to Malus domestica Borkh. branches showed that achieving hydraulic steady state takes considerable time (up to 300 min) and that time to reach steady state increased with declining xylem water potentials. During each experimental run, K-h and xylem water potentials dynamically increased, which was supported by X-ray computed microtomography visualizations of embolism refilling under both high- (8 kPa) and low-pressure (2 kPa) heads. Supplying pressurized water can hence cause artificial refilling of vessels, which makes it difficult to achieve a truly stable K-h in partially embolized xylem.