Hydraulics of Vascular Water Transport

Abstract

The science of plant water transport is equal parts of physics and biology. Plants have evolved a complex wick system that harnesses the cohesive hydrogen bond energy of liquid water and suppresses the heterogeneous nucleation of caVita- tion. Trade-offs between making the wick safe against cavitation and implosion, yet efficient in moving water, result in the process being limiting to plant perfonnance. Cavitation limits the range of negative pressures that can be harnessed to move water, and the hydraulic conductance of the wick limits the flow rate that can be moved at a given negative pressure gradient. Both limits constrain C02 uptake via the water-for- carbon trade-off at the stomatal interface. Research in the area concerns the mechan- isms of cavitation, its reversal by embolism repair, consequences for plant ecology and evolution, and the coupling of water transport to plant productivity. Very little is known ofthe molecular biology underlying xylem physiology. 1