Hydrophilic Surface and End-Walls in Vessels Help Water Ascend

摘要

How water ascends in tall trees is far from fully understood. At present, each theory suffers accusations of being inadequate and misleading. They share, none the less, one consensus that many air bubbles are present in xylem vessels, a feature believed to interrupt water lifting due to embolisms. Here, using a microfluidic technology to mimic xylem vessels in trees, we show that air bubbles are formed spontaneously when water ascends in artificial vessels with super-hydrophilic surface and end-wall pits. Contrary to the traditional believe, we show that air bubbles together with end-wall structures of xylem help water to ascend to a level that cannot be achieved in a continuous water column; the water ascent persists even in the presence of a small pressure gradient despite large numbers of air bubbles. The result may contribute a new explanation for water movement in higher plants.