Báo cáo lâm nghiệp: "Ultrasound acoustic emission in water-stressed Picea abies Karst"

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Ultrasound acoustic emission in water-stressed plants of Picea abies Karst. A. Raschi 2 M. J. Grace 1 Borghetti 1 C.N.R. lMGPF, Via S. Bonaventura. 13-50145 Florence, Italy, S. onaventura, C.N.R. 2 IATA, P. le delle Cascine, 18-50144 Florence, ttaly, and Department 3 of Forestry and IYat. Res., Darwin Building, Mayfield Road, Edinburgh EH9 3JU, U.K. Introduction Potted 5 yr old plants of Picea abies were used, 10 of them were irrigated on a daily basis, while 10 others were assigned to drought treatment, witholding water from them during the periods It is widely known that cavitative events 15-21 July, 8-14 August and 16-25 August taking place in woody stems can be de- 1987. Measurements were made from dawn to tected by monitoring acoustic emissions sunset on July !!1, July 30, August 25 and Sep- due to the vibrations of the xylem vessel tember 10. Xylem water potential was mea- walls. If operating at audio frequencies sured with a pressure chamber every 2 h on plants among the 10 belonging to each group. (Milburn and Johnson, 1966), noise from The 6 remaining plants in each treatment were the surroundings can mask the faint used for measurements of acoustic emission sounds coming from wood elements. The rate using a broad band Bruel and Kjaer model use of sensors operating at ultrasonic 8312 sensor, and a counting device similar to the one described by Sandford and Grace frequencies (Tyree and Dixon, 1983) over- (1985), modified. The transducer was pressed comes this problem. We report the occur- on the stem using a spring-loaded handpiece, rence of ultrasonic acoustic emissions for a period of :5 min; the stem had been pre- from the stems of potted saplings of pared by removing the bark; the exposed sur- Picea abies Karst. during the summer, face was coated with petroleum jelly to prevent water loss, and an ultrasound gel was applied relating these to transpiration rate and to improve acoustic transmission. On the same water potential, since this technique has plants, the transpiration rate was measured gra- rarely been used under field conditions vimetrically and stomatal conductance was and water stress is a major limiting measured using a porometer. Leaf area of each plant was measured at the end of the experi- factor of wood production in mediter- ment. ranean climates. Results Materials and Methods On July 21 (Fig. 1 a), the drought-treated The experiment took place in the nursery of the School of Forestry of the University of Firenze. plants were stressed, as shown by physio-
data. The difference in acoustic ward, the stressed plants were watered logical emission rate between these plants and until July 30, when the measurements the well-watered plot is also evident. After- The differences repeated. (Fig. 1 b). were
dis- dimensions of tracheids, the listening in physiological data and acoustic emis- tance of the sensor and the average num- sion rate between the recovered and the ber of cavitations detected on a typical well-watered plants were not statistically sunny day, suggests that after the 3 cycles significant. During August, the stressed of drought, the hydraulic conductance plants were subjected to 2 periods of should be substantially reduced. In fact, stress; after that, the abovementioned on September 10, the conductance of pre- parameters were measured again on viously stressed plants was about 28% of August 25 (Fig. 1 c). The physiological that of well-watered plants. data show that water stress was greater than before and the acoustic emission rate was much higher. Measurements were made again on September 10, after a long Conclusions recovery period (Fig. 1d). The physiologi- cal parameters show the different be- haviors of the 2 plots: transpiration and The ultrasound sensor seems to be a use- stomatal conductance did not recover ful new tool for studying water stress in completely in the stressed one, but the field plants, although the use of data in a acoustic emission rate was very low for all quantitative manner is still difficult. How- the plants. ever, it seems that ultrasound sensing in woody plants has progressed to the point where the output from the sensor might be used for practical purposes. Discussion Since acoustic emission is a consequence References of cavitation events taking place in xylem elements, and it is widely accepted that each acoustic event corresponds to the Milburn J.A. & Johnson R.P.C. (1966) The conduction of sap. 11. Detection of vibrations cavitation of water in one tracheid, a produced by sap cavitation in Ricinus stem. reduction of hydraulic conductance can be Planta 69, 43-52 expected as a consequence of cavitation Sandford A.P. & Grace J. (1985) The measure- due to water stress. To assess the magni- ment and interpretation of ultrasounds from tude of changes in hydraulic resistance, 1 woody stems. J. Exp. Bot. 36, 298-311 we plotted the transpiration rate against & Dixon M.A. (1983) Cavitation Tyree M.T. the water potential (Fig. 2), obtaining the events in Thuja occidentalis L.? Ultrasonic hydraulic resistance as the slope of this acoustic emissions from the sapwood can be Plant PhysioL 72, 1094-1099 measured. relationship. A calculation based on the