A new method of sap flow rate determination in stems of adult trees is described in which mass flow (the transpiration flux in the present case) is estimated from a heat-transfer measurement. The device used includes a couple of thermometers in a differential connection and plate electrodes, through which a controlled heat input flows into a denned studied segment of the xylem. The present method was tested first with a laboratory simulating system, then with the stem of a living adult treePrunus avium L. The data are registered continually and automatically; continuous measurement of sap flow rate of long duration with a greater number of trees is thus made possible.AbstractByla navržena nová metoda stanovenÍ vedenÍ vody v kmeni adultnÍch stromÜ, založená na principu mčřeni hmotného toku (transpiraeniho proudu) na základĚ prenosu tepla. ZařÍzčnÍ se skládá z dvojice diferenciálnč zapojených teplomčrů a deskových elektrod, kterými je přiváděn kontrolovaný tepelný výkon do zkoumané části aktivnÍho xylemu (definovaného segmentu), Navrženà metoda byla vyzkoušena na simulátoru v laboratornÍch podminkàch a na kmeni živého adultnÍho stromuPrunus avium L. Data jsou plnč automaticky a kontinuálnč registre-vána: to umožňuje kontinuámÍ sledovànÍ intensity transpiračnÍho proudu po dlouhá časová údobÍ simultánč u vĚtšÍho počtu stromů.
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