Radial stem flow and its importance when measuring xylem hydraulic conductance

Abstract

Despite the importance of water transport efficiency for plant productivity, the current methods to measure the hydraulic conductance in stem segments are limited and can be tricky. These measurements may be unstable for several hours and there are no satisfactory procedures that allow choosing the moment to get reliable measures. Such instability may be generated by background flow, when there is a flow even without applying water pressure to induce the axial flow. Underlying mechanisms related to background flow are still unknown and based on available literature, we propose that the background flow is affected, or even explained, by the radial water flow and tissue capacitance. For this reason, both phenomena are fundamental for understanding plant water transport, the coupling between the phloem and xylem, and water relations under drought conditions. Besides addressing this issue, we suggest ways to study the radial water flow and capacitance in stem segments.