Measuring plant hydraulic conductance and xylem vulnerability under close to natural conditions

Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is cavitation, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures. Various physical characteristics of the xylem influence the efficiency of transport and the vulnerability to cavitation.

Here we explore possibilities to measure hydraulic conductance and induce cavitation under close to natural conditions. We designed a very simple “artificial plant” consisting of a root and a transpiring membrane, equipped with pressure and flow meters, where a twig can be inserted in the flow path to measure its hydraulic conductance. Attempts to induce cavitation resulted in surprising results, provoking new questions on the role of xylem structural traits and their relevance for water transport in plants.