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. | 342s Ann. Sci. For. 1989 46 suppl. 342s-345s Forest Tree Physiology E. Dreyer etal. eds. Elsevier INRA Detection of cavitation events upon freezing and thawing of water in stems using ultrasound techniques A. Raschi1 . Scarascia- Mugnozza2 R. Valentini2 and c. Vazzana3 . A 50144 Firenze . 2 1st. Biol. Selvicolturale - Univ della Tuscia Viterbo and 3 Dipt di Agronomia e Produzioni Erbacee Univ di Firenze delle Cascine 18 Firenze Italia Introduction In recent years renewed attention has been paid to cavitative events occurring in plants subjected to water stress. This has been a result of the creation of new techniques based on the detection of sounds Milburn 1973 or more reliably ultrasounds Tyree and Dixon 1983 emitted by the plant as a consequence of the vibration of cavitating conducting elements. The results obtained so far show that the development of emboli is a phenomenon that occurs much more frequently than was supposed and takes place at a different frequency in different species. Indeed several observations summarized by Zimmermann 1983 suggest that cavitation should take place upon the freezing and the thawing of water in vessels. In fact the existence of cavitative events as a consequence of cycles of freezing and thawing has been evidenced by several authors Scholander eta . 1955 Hammel 1967 Sucoff 1969 who showed the existence of permanent damage to the conductive system in some species. To date research has investi gated the consequences of the above mentioned cycles without directly demonstrating the cavitative events as they were taking place. Moreover most of the work has been carried out on conifers which according to the literature are less damaged than angiosperms. In this preliminary text we examine the differences in the ultrasound emissions that exist between a coniferous Araucaria excelsa and a broad-leafed Eucalyptus occiden-talis tree during lowering and rising of the temperature. Materials and Methods The experiment .
