Short-term effects of potassium fertilization on the hydraulic conductance of Laurus nobilis L

This study reports experimental evidence on the effect of short term potassium fertilization on potassium uptake, tissue concentration and hydraulic conductance of pot-grown laurel plants. Potassium uptake and loading into the xylem of laurel seedlings increased within 24 h from fertilization. Potassium was not accumulated in roots and leaves, but the [K+] of xylem sap was 80% higher in fertilized plants (+K) than in potassium starved plants (-K), likely as a result of recirculation between xylem and phloem. This increase in xylem sap [K+] resulted in a 45% increase in transpiration rate, a 30% increase in plant hydraulic conductance (Kplant) and a 120% increase in leaf specific conductivity of the shoot (kshoot ). We suggest that this increase was due to ion-mediated up-regulation of xylem hydraulic conductance, possibly caused by the interaction of potassium ions with the pectic matrix of intervessel pits. This enhancement of hydraulic conductance following short-term potassium fertilization is a phenomenon that can be of advantage to plants for maintaining cell turgor, stomatal aperture and gas exchange rates under moderate drought stress and these data provide additional support to the important role of potassium nutrition in agriculture and forestry.