Abstract: | Legge, N. J. 1985. Water movement from soil to root investigatedthrough simultaneous measurement of soil and stem water potentialin potted trees.J. exp. Bot. 36: 15831589. Osmotic tensiometers implanted in the stems of three mountainash (Eucalyptus regnans F. Muell.) saplings growing in largeplastic bins recorded stem water potential, w, while soil waterpotential, w, was simultaneously recorded by instruments nearthe trees' roots and in the surrounding root-free soil Earlyin a drying cycle, with the soil still wet, the diurnal variationin 1, was often slight, despite diurnal variations in u approaching2.0 M Pa. Late in a drying cycle the diurnal fluctuations in1, and u were very similar although changes in 1, still laggedup to 1.5 h behind changes in u. 1values at this time occasionallyreached 3.0 MPa with no apparent damage to the treesWatering the bins in daytime led to a response in 1, valueswithin about 5 min, whereas u, values did not respond for afurther 20 min. u values then rose rapidly but after only 1h began to decline again, while 1, values remained at or nearsaturation for the rest of the day. Water uptake hypotheseswhich attribute an important role to a soil-root interface resistanceare not supported by these data Key words: Soil water potential, penrhizal gradients |