Potencials of sap flow evaluation by means of acoustic emission measurements

Abstract

The work deals with measurement techniques of water conducting system in the trees. Water conducting system (including xylem and phloem) indicates its importance for related physiological processes. There are still problems how to measure its functioning (which variables and how), especially in the open field (e.g., forests and orchards) in order to get maximum information about it. Simple band dendrometers measuring seasonal dynamics of stem growth have been already applied for many years, being gradually replaced by their more sophisticated electronic versions most recently. The sap flow is a suitable variable, because it links roots and crowns and provide information about transporting the largest amount of mass in plants, which can be decisive for their behavior. Following pioneering work in the last century (Huber, 1932), many types of sap flow measurement methods based on a variety of principles (e.g., thermodynamic, electric, magneto-hydrodynamic, nuclear magnetic resonance, etc.) have been described. Only a few of these, particularly those based on thermodynamics, have been widely used in field-grown trees. E.g., heat pulse velocity system developed by Green (1998) and Cohen et al. (1981). Heat ratio method also works with pulses, but interpreted the data in more sophisticated way (Burgess, 2001). Widely used is a simple heat-dissipation method (Granier, 1985). Direct electric heating and internal sensing of temperature was applied in the trunk heat balance method (Čermák et al., 1973, 1976, 1982, 2004; Kučera et al., 1977; Tatarinov et al., 2005). The heat field deformation method is based on measurement of the deformation of the heat field around a needle-like linear heater (Nadezhdina et al., 1998, 2002, 2006; Čermák et al., 2004).Another important variable is water potential, which could be measured in the past only periodically on selected pieces of plant material using pressure (Scholander) bomb, but most recently also continuous measurements became possible due to application of psychrometric method (Dixon and Tyree, 1985). There exist also other physical variables carrying important information, which can be measured using different principles. This includes e.g., acoustic methods, which can detect quantitative variation of pulses occurring during cavitation events, associated with interruptions of water columns in vessels. This must not necessarily be a single source of acoustic emissions. In this study we are focused on a general description of acoustic events measurable in a wide range of their spectrum. The first aim was to detect such signals and the second to learn them and gradually analyze in order to better understand the associated processes causing their occurrence and their relations to plant life.

Detection of Acoustic Emission Characteristics of Plant According to Water Stress Condition

“…From this situation, we supposed these detected AE signals were established from cavitation event in xylem on plant exposed to severe soil water deficit. This result is consistent with the other publications (Jia et al, 2006 andČerný et al, 2011) which reported that AE signal occurrence in water stressed plant remained higher than that of in well-watered plant because of soil dehydrated. For detecting AE signals of M1 and M2 by AE sensors, it was found that recieving AE signals of AE sensor in M2 was better that that of AE sensor in M1.…”

“…These results revealed that very few AEs occurred in well-watered plant, whereas great amounts of AEs were detected during the drought cycle. The correlation of sap flow in trees and acoustic emission signals were discussed by Černý M. et al (2011) andMazal P. et al (2012). They confirmed that detected AE signals from trees reflected embolic event in vessels occuring during rapid changes in sap flow rate.…”