5 - Leaf hydraulics and its implications in plant structure and function

Abstract

The field of leaf hydraulics is still in discovery phase, and new work is needed to remove the many unknowns. Each year more than 40 trillion tons of water move through plant leaves, about 10% of the water leaving the planet's surface, two thirds of that from land. This component of water's passage through the hydrologic cycle, the microhydrological process inside the leaf, contains many outstanding mysteries. Water flow through leaves has important implications for understanding whole-plant hydraulics and plant growth, as well as leaf structure, function, and ecology. Since the late 1990s, research has increased, including new perspectives from physics, anatomy, modeling, and ecology. This chapter describes the importance of the leaf in determining whole-plant hydraulic conductance, which can strongly influence gas exchange and growth. Next, it examines the basis of leaf hydraulic conductance in the pathways of water movement in the leaf. In the following sections, it describes how leaf hydraulic conductance is linked with other aspects of leaf structure/function, including venation design, leaf shape, water storage, and structural features important in plant carbon economy and drought tolerance. The chapter surveys recent work on the dynamics of leaf hydraulic conductance across plant growth conditions, as well as diurnally, and across leaf ages.