Ultrasound acoustic emissions from dehydrating leaves of deciduous and evergreen trees

Abstract

While drying, detached leaves produced ultrasound acoustic emissions (UAE) comparable to emissions from stem and twig wood. Experiments on Ilex aquifotium L. showed that the main source of these signals was cavitation in the veins, to which conduits and fibres probably both contributed. Regions of the leaf blade with abundant mesophyll and only small veins emitted few signals. More signals were counted on the adaxial side of the midrib than on the abaxial one and on the proximal third than on the distal one, in accordance with the anatomical structure. Sound attenuation was pronounced. Eight species were compared with respect to cavitation behaviour, field water relations and pressure-volume curves, and tbe data showed differences in cumulative number of events and resistance of leaves to cavitation. Data were generally in good agreement witb anatomical structure and habitat preferences. The number of signals per conduit counted on cross-sections was in some leaves much higher than unity, which suggests short xylem elements or an acoustic activity of cells other than conduits. There was no correlation between cavitation threshold or cumulative number of signals and the degree of sclerophylly; unexpectedly, there was a correlation between tbe cumulative number of signals at a water potential of-1-3 MPa and the bulk modulus of elasticity.

Acoustic Emissions to Measure Drought-Induced Cavitation in Plants

“…Further scope of this review is, however, on its application in the detection of drought-induced cavitation in plants. During dehydration of fresh plant material, AE signal detection was found to be a valid method to measure cavitation in woody branches [35], leaves [56], herbaceous stems [57] and sap wood sections [49], while others found a poor correspondence between hydraulic and acoustic measurements [58,59]. Especially in angiosperm species, the continued AE activity after loss of most of the hydraulic conductivity was a great cause of concern [31,60].…”

Refilling of Embolized Vessels in Young Stems of Laurel. Do We Need a New Paradigm?1

“…The threshold xylem pressure for cavitation is close to the typical midday xylem pressure of many species in the field (Kikuta et al, 1997). Such a narrow safety margin (Sperry, 1995) is intrinsically dangerous for plant survival under adverse environmental conditions but might be of some advantage in buffering leaf water status (Dixon et al, 1984;Salleo et al, 1997) and in inducing stomatal closure (Sperry, 1995).…”

“…The cavitation (droughtinduced embolism) of xylem has been detected in stems (Cochard and Tyree, 1990), leaves (Kikuta et al, 1997), and roots (Mencuccini and Comstock, 1997) and has appeared to limit effectively the possible distribution areas of plant species (Cochard et al, 1992). For example, the vulnerability of Holm oak to xylem embolism caused by both drought and freeze stress (Lo Gullo and Salleo, 1993) provides a convincing explanation for the distribution versus elevation and latitude of this species (Pignatti, 1982) in the Mediterranean region.The threshold xylem pressure for cavitation is close to the typical midday xylem pressure of many species in the field (Kikuta et al, 1997). Such a narrow safety margin (Sperry, 1995) is intrinsically dangerous for plant survival under adverse environmental conditions but might be of some advantage in buffering leaf water status (Dixon et al, 1984;Salleo et al, 1997) and in inducing stomatal closure (Sperry, 1995).…”

“…The cavitation (droughtinduced embolism) of xylem has been detected in stems (Cochard and Tyree, 1990), leaves (Kikuta et al, 1997), and roots (Mencuccini and Comstock, 1997) and has appeared to limit effectively the possible distribution areas of plant species (Cochard et al, 1992). For example, the vulnerability of Holm oak to xylem embolism caused by both drought and freeze stress ) provides a convincing explanation for the distribution versus elevation and latitude of this species (Pignatti, 1982) in the Mediterranean region.…”

Drought resistance of Quercus pubescens as a function of root hydraulic conductance, xylem embolism and hydraulic architecture

“…Most of these studies report seasonal and diurnal changes of water relations parameters measured in leaves and stems such as leaf water potential (ψ L ), conductance to water vapour (g L ), relative water content (RWC) and, more recently, vulnerability to xylem cavitation of stems (Tyree & Sperry, 1989 ;Lo Gullo & Salleo, 1993) and leaves (Kikuta et al, 1997). The recent introduction of novel instrumentation (High Pressure Flow Meter, HPFM) measuring hydraulic parameters of roots growing in the field (Tyree et al, 1995), has made it possible to obtain parallel recordings of ψ L , g L , RWC and root hydraulic *Author for correspondence (tel.…”