Changes of xylem sap ionic content and stem hydraulics in response to irradiance in Laurus nobilis

This is the authors' abstract. We don't add key points for this paper.

This study reports experimental evidence for light-mediated changes of stem hydraulic conductance (K(stem)) in field-grown laurel plants. Field measurements based on the evaporative flux method revealed that sun-exposed branches had 60% higher K(stem) with respect to shade-exposed branches. Xylem sap potassium concentration was approximately 3 mM as recorded in shaded branches and up to 12 mM in illuminated ones. Such a difference in [K(+)] proved to induce significant increase in xylem hydraulic conductance of excised twigs when artificially perfused with various solutions, as a likely consequence of the interaction of cations with the pectic matrix of pit membranes (the so-called 'ionic effect'). We propose that this mechanism provides plants with a large potential for fine regulation of water flow towards different parts of the canopy exposed to different environmental conditions with the result of optimizing light and water utilization.