Effect of potassium fertilization on the hydraulic conductance of laurel plants

The effect of potassium fertilization on hydraulic conductance was tested in 2-year-old potted laurel seedlings, grown in a greenhouse at the Botanical Garden of Palermo. Plants were divided into a control group (+K) and a potassium starved group (-K). A set of randomly chosen -K plants received irrigation with 25 mM KCl (KCl plants) 24 hours before measurements, to test the short term effect of potassium fertilization. Measurements were carried out in July and October 2008. Whole-plant hydraulic conductance was measured by the evaporative flux method; root and shoot hydraulic conductance were measured by the vacuum chamber. Potassium availability or season did not significantly affect leaf water potential, leaf conductance to water vapour, whole plant hydraulic conductance or root hydraulic conductance. In July, leaf specific conductivity (= hydraulic conductance divided by leaf area, kL) was about 60 % lower in +K and -K plants than in KCl plants, but in October this significant difference disappeared. The possible role of potassium availability on shoot and leaf specific hydraulic conductivity is discussed in terms of the hydrogel effect in pit membranes of stem vessels.