Department of Botany, University of Innsbruck, Sternwartestrasse 15, Innsbruck, Austria.
Tree Physiol. 2011 Jan;31(1):59-67. doi: 10.1093/treephys/tpq099.
Ultrasonic emission (UE) testing is used to analyse the vulnerability of xylem to embolism, but the number of UEs often does not sufficiently reflect effects on hydraulic conductivity. We monitored the absolute energy of UE signals in dehydrating xylem samples hypothesizing that (i) conduit diameter is correlated with UE energy and (ii) monitoring of UE energy may enhance the utility of this technique for analysis of xylem vulnerability. Split xylem samples were prepared from trunk wood of Picea abies, and four categories of samples, derived from mature (I: earlywood, II: 30-50% latewood, III: >50% latewood) or juvenile wood (IV: earlywood) were used. Ultrasonic emissions during dehydration were registered and anatomical parameters (tracheid lumen area, number per area) were analysed from cross-sections. Attenuation of UE energy was measured on a dehydrating wood beam by repeated lead breaks. Vulnerability to drought-induced embolism was analysed on dehydrating branches by hydraulic, UE number or UE energy measurements. In split samples, the cumulative number of UEs increased linearly with the number of tracheids per cross-section, and UE energy was positively correlated with the mean lumen area. Ultrasonic emission energies of earlywood samples (I and IV), which showed normally distributed tracheid lumen areas, increased during dehydration, whereas samples with latewood (II and III) exhibited a right-skewed distribution of lumina and UE energies. Ultrasonic emission energy was hardly influenced by moisture content until ∼40% moisture loss, and decreased exponentially thereafter. Dehydrating branches showed a 50% loss of conductivity at -3.6 MPa in hydraulic measurements and at -3.9 and -3.5 MPa in UE analysis based on cumulative number or energy of signals, respectively. Ultrasonic emission energy emitted by cavitating conduits is determined by the xylem water potential and by the size of element. Energy patterns during dehydration are thus influenced by the vulnerability to cavitation, conduit size distribution as well as attenuation properties. Measurements of UE energy may be used as an alternative to the number of UEs in vulnerability analysis.
超声发射 (UE) 测试用于分析木质部对栓塞的脆弱性，但 UE 的数量通常不能充分反映对水力传导性的影响。我们监测脱水木质部样本中 UE 信号的绝对能量，假设 (i) 导管直径与 UE 能量相关，(ii) 监测 UE 能量可能会增强该技术在木质部脆弱性分析中的效用。从云杉树干中制备分裂木质部样本，并使用来自成熟木（I：早材，II：30-50%晚材，III：>50%晚材）或幼木（IV：早材）的四个样本类别。在脱水过程中记录超声发射，并从横截面分析解剖参数（管腔面积、面积内的数量）。通过重复折断铅来测量脱水木梁上 UE 能量的衰减。通过液压、UE 数量或 UE 能量测量分析脱水枝条上干旱诱导栓塞的脆弱性。在分裂样本中，UE 数量的累积数量与每个横截面的管胞数量呈线性相关，UE 能量与平均管腔面积呈正相关。表现出正态分布管腔面积的早材样本（I 和 IV）的超声发射能量在脱水过程中增加，而具有晚材（II 和 III）的样本表现出管腔和 UE 能量的右偏分布。在水分含量约为 40%之前，超声发射能量几乎不受水分含量的影响，此后呈指数下降。在液压测量中，脱水枝条在 -3.6 MPa 时表现出 50%的传导率损失，而在基于信号累积数量或能量的 UE 分析中，分别在 -3.9 和 -3.5 MPa 时表现出 50%的传导率损失。空化导管发出的超声发射能量由木质部水势和元素大小决定。因此，脱水过程中的能量模式受空化脆弱性、导管尺寸分布以及衰减特性的影响。UE 能量的测量可以替代脆弱性分析中的 UE 数量。
