Propagating ice front induces gas bursts and ultrasonic acoustic emissions from freezing xylem
Propagating ice front induces gas bursts and ultrasonic acoustic emissions from freezing xylem
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DOI：
10.1093/treephys/tpz123
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发表时间：
2020-02-01
期刊：
影响因子：
4
通讯作者：
Mayr, Stefan
中科院分区：
文献类型：
--
作者：
Lintunen, Anna;Losso, Adriano;Mayr, Stefan
植物木质部中冰的形成和传播是一个复杂的过程。在木质部汁液冻结期间，溶解在液体汁液中的气体由于其在冰中的溶解度低而被挤出冰晶格，并且在冰-液界面处引起木质部汁液的过饱和以及低水势（Psi）。冰锋附近的气体过饱和可能导致气泡形成，并可能导致空化和/或从分支中排出的气体破裂。在这项研究中，我们研究了与冻结相关的气体爆发和超声波发射（AE）的起源和动力学，这表明空化现象。云杉 (L.) H.喀斯特。和 Salix caprea L. 枝段在温度测试室中暴露于霜冻循环，并记录 CO2 流出（指示气体爆发）和 AE。冻结时，观察到的气体爆发有三分之二来自木质部，只有三分之一来自树皮。在发生气体爆炸的同时，检测到了 AE。分支 Psi 影响气体爆发和 AE，在饱和和干燥样品中气体爆发较高，但相关 AE 仅在后者中。反复的霜冻循环导致气体爆发量和AE活动减少。实验表明，冷冻木质部中不断扩大的冰锋是观察到的气体爆发和 AE 的原因，而分支 Psi 影响了这两个过程。结果还表明，气体破裂和空化是由冰形成独立引起的，尽管两者都可能与冻结过程中的气泡动力学有关。
Ice formation and propagation in the xylem of plants is a complex process. During freezing of xylem sap, gases dissolved in liquid sap are forced out of the ice lattice due to their low solubility in ice, and supersaturation of xylem sap as well as low water potential (Psi) are induced at the ice-liquid interface. Supersaturation of gases near the ice front may lead to bubble formation and potentially to cavitation and/or to burst of gases driven out from the branch. In this study, we investigated the origin and dynamics of freezing-related gas bursts and ultrasonic acoustic emissions (AEs), which are suggested to indicate cavitation. Picea abies (L.) H. Karst. and Salix caprea L. branch segments were exposed to frost cycles in a temperature test chamber, and CO2 efflux (indicating gas bursts) and AEs were recorded. On freezing, two-thirds of the observed gas bursts originated from the xylem and only one-third from the bark. Simultaneously with gas bursts, AEs were detected. Branch Psi affected both gas bursts and AEs, with high gas burst in saturated and dry samples but relevant AEs only in the latter. Repeated frost cycles led to decreasing gas burst volumes and AE activity. Experiments revealed that the expanding ice front in freezing xylem was responsible for observed gas bursts and AEs, and that branch Psi influenced both processes. Results also indicated that gas bursts and cavitation are independently induced by ice formation, though both may be relevant for bubble dynamics during freezing.