Heidelberg 1999 – wissenschaftliches Programm
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UP: Umweltphysik
UP 4: Agrarphysik
UP 4.5: Vortrag
Montag, 15. März 1999, 17:30–17:45, KO
THz-Imaging: A noninvasive method to study water flow in plant leaves — •N.E. Hecker1, I.H. Libon1, M. Hempel1, M. Koch1, J. Fromm2, and J. Feldmann1 — 1Lehrstuhl für Photonik und Optoelektronik, Universität München, D-80799 München — 2Institut f"ur Holzforschung, Universität München, D-80797 München
New noninvasive methods to determine water concentration and flow in living plants to supplement other techniques such as NMR are desired. With the recent development of bright, THz-frequency light sources, a new technique allowing the spatial mapping of water concentration in plant leaves has been made possible. Because in plants, water is mostly responsible for absorption in the THz frequency range, a simple measurement of the THz-light transmission provides a direct determination of water concentration. Scanning a leaf through a focussed THz beam allows water concentration to be determined with a spatial resolution limited only by diffraction [1]. Using THz-pulses generated by an ultrafast photoconductive switch [2], we have investigated the absolute change in water concentration in leaves of several plants after watering. Spatial resolved images were collected every 15 minutes over hours to quantitatively analyse the increase in water. Plant leaves were chosen to include tracheid and vessel diameters varying from 10 - 150 µ m. Preliminary results show that water flow into the leaves is largest for plants with the largest xylem elements which is in agreement with other measurements [3]. [1] B.B. Hu and M.C. Nuss, Opt. Lett. 20, 1716 (1995). [2] D. Grischkowsky et al., J. Opt. Soc. Am. B 7, 2006 (1990). [3] M.H. Zimmermann, Xylem Structure and the Ascent of Sap, Springer Verlag, 1983.