Vergeynst Lidewei L, Sause Markus G R, De Baerdemaeker Niels J F, De Roo Linus, Steppe Kathy
Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
Experimental Physics II, Institute for Physics, University of Augsburg, D-86135 Augsburg, Germany.
Tree Physiol. 2016 Jun;36(6):786-96. doi: 10.1093/treephys/tpw023. Epub 2016 Apr 19.
The formation of air emboli in the xylem during drought is one of the key processes leading to plant mortality due to loss in hydraulic conductivity, and strongly fuels the interest in quantifying vulnerability to cavitation. The acoustic emission (AE) technique can be used to measure hydraulic conductivity losses and construct vulnerability curves. For years, it has been believed that all the AE signals are produced by the formation of gas emboli in the xylem sap under tension. More recent experiments, however, demonstrate that gas emboli formation cannot explain all the signals detected during drought, suggesting that different sources of AE exist. This complicates the use of the AE technique to measure emboli formation in plants. We therefore analysed AE waveforms measured on branches of grapevine (Vitis vinifera L. 'Chardonnay') during bench dehydration with broadband sensors, and applied an automated clustering algorithm in order to find natural clusters of AE signals. We used AE features and AE activity patterns during consecutive dehydration phases to identify the different AE sources. Based on the frequency spectrum of the signals, we distinguished three different types of AE signals, of which the frequency cluster with high 100-200 kHz frequency content was strongly correlated with cavitation. Our results indicate that cavitation-related AE signals can be filtered from other AE sources, which presents a promising avenue into quantifying xylem embolism in plants in laboratory and field conditions.
干旱期间木质部中空气栓塞的形成是导致植物因水力传导率丧失而死亡的关键过程之一，这也极大地激发了人们对量化空化脆弱性的兴趣。声发射（AE）技术可用于测量水力传导率损失并构建脆弱性曲线。多年来，人们一直认为所有的声发射信号都是由处于张力状态的木质部汁液中气体栓塞的形成产生的。然而，最近的实验表明，气体栓塞的形成并不能解释干旱期间检测到的所有信号，这表明存在不同的声发射源。这使得使用声发射技术测量植物中栓塞的形成变得复杂。因此，我们使用宽带传感器分析了在实验台上脱水期间葡萄（Vitis vinifera L. 'Chardonnay'）枝条上测量的声发射波形，并应用自动聚类算法来寻找声发射信号的自然聚类。我们利用连续脱水阶段的声发射特征和声发射活动模式来识别不同的声发射源。基于信号的频谱，我们区分了三种不同类型的声发射信号，其中频率在100 - 200 kHz范围内较高的频率聚类与空化密切相关。我们的结果表明，可以从其他声发射源中过滤出与空化相关的声发射信号，这为在实验室和田间条件下量化植物木质部栓塞提供了一条有前景的途径。
