Abstract:

Long-distance water transport in plants is an important issue in plant physiology and eco-physiology. The recent development of the Xylem Pressure Probe for direct measurement of pressure in individual xylem elements of intact, transpiring plants elicited challenges to the long-standing, widely accepted Cohesion-Tension (C-T) Theory. These challenges instigated debate in the field of plant physiology over mechanisms of long-distance water transport. The challengers and proponents of the C-T theory mutually criticized the Pressure Bomb and the Xylem Pressure Probe technology, and they debated over all three elements of C-T theory (high tension in xylem units; pressure gradients over tree height; the continuous water column in xylem vessels) by reviewing literature and providing physical bases. The debate has cooled down. As a result, the C-T theory has not been discredited while the raised questions in the debate remain mainly unanswered and call for future researches.

Key words: cohesion-tension theory, xylem pressure probe, pressure bomb, long-distance water transport, xylem cavitation