Báo cáo lâm nghiệp: Detection of cavitation events upon freezing and of water in stems using ultrasound technique

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Detection of cavitation events upon freezing and of water in stems using ultrasound techniques...
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Báo cáo lâm nghiệp: "Detection of cavitation events upon freezing and of water in stems using ultrasound technique"Detection of cavitation events upon freezing and thawingof water in stems using ultrasound techniques R. Valentini 2A. Raschi G.E. Scarascia- 1 Mugnozzaand C. Va zana 3 C. Vazzana 31 C.N.R.-I.A. T.A., 50144 Firenze,2 Biol. Selvicolturale - Univ. della Tuscia, Viterbo, and Ist.3 Dipt. di Agronomia e Produzioni Erbacee, Univ. di Firenze, P.le delle Cascine, i8, Firenze, Italia consequences of the aboveIntroduction gated the cycles, without directly de- mentioned monstrating the cavitative events as theyIn recent years, renewed attention has were taking place. Moreover, most of thebeen paid to cavitative events occurring in work has been carried out on conifers,plants subjected to water stress. This has which, according to the literature, are lessbeen a result of the creation of new tech- damaged than angiosperms. In this pre-niques based on the detection of sounds liminary text, we examine the differences ultra- reliably,(Milburn, 1973) or, more in the ultrasound emissions that exist be-sounds (Tyree and Dixon, 1983) emitted tween a coniferous (Araucaria excelsa)by the plant as a consequence of the and a broad-leafed (Eucalyptus occiden-vibration of cavitating conducting ele- talis) tree during lowering and rising of thements. The results obtained so far show temperature.that the development of emboli is a phe-nomenon that occurs much more fre-quently than was supposed, and takesplace at a different frequency in different Materials and Methodsspecies. Indeed, several observations,summarized by Zimmermann (1983), sug-gest that cavitation should take place The experiment was carried out in the laborato- ry of the Agronomy Department of the Universi-upon the freezing and the thawing of ty of Firenze, Italy, using 3 yr old potted plantswater in vessels. In fact, the existence of of E. occidentalis Endl., and 4 yr old excisedcavitative events as a consequence of lateral branches of A. excelsa R. Br. All plantscycles of freezing and thawing has been had been acclimated for 2 wk in a growth cham- ber and none of them had experienced waterevidenced by several authors (Scholander freezing during the previous months; stress oret al., 1955; Hammel, 1967; Sucoff, 1969), water potential, measured by pressure xylemwho showed the existence of permanent chamber on all plants before the experiments,damage to the conductive system in some ranged between 0.07 and 0.11 MPa. The potsspecies. To date, research has investi- of Eucalyptus plants were enclosed in a thermal Resultsinsulated box to prevent soil freezing. The cutextremity of Auracaria branches, recut underwater, was kept immersed in water and en-closed in an insulated box. Plant stems were Fig. 1, the typical behavior of ultrasound Infrozen in a top loading freezer, whose top cover pulses as a function of stem temperaturehad been substituted with expanded poly- Before ice for- in is Eucalyptus reported.styrene material. A hole had been cut in the mation, which occurred at an averagenew cover in order to allow the distal part of thesample, with all leaves to be kept at room supercooling temperature of -4.5°C, onlytemperature, enclosed in a black plastic bag. a few isolated events were recorded. ATemperature was lowered at a rate of 5°C per considerable emission rate appearedhour. To measure the acoustic emission rate, a several minutes after ice formation andBruel and Kjaer 8312 broad band sensor wasclamped in a handpiece to the lower part of the the maximum was detected at the loweststem, which had previously been prepared by temperature reached (-8°C). As the tem-removing a small window of bark to expose the ...