Original article Comparison of methods to quantify loss of hydraulic conductivity in Norway spruce

Abstract – • Percent loss of hydraulic conductivity (PLC) is an important measure in plant water relations, but the available methods differ and results have rarely been compared. •We compared PLC measured in Norway spruce (Picea abies) by quantifying conductivity before and after removing emboli, either by flushing with high water pressure or by infiltration under a partial vacuum, with relative water loss and staining conductive xylem to test advantages and possible problems of commonly applied methods. • Infiltration removed nearly all gas from sections of drought-stressed and unstressed twigs, and flushing and infiltration efficiently removed emboli. Infiltration appears less prone to producing clogged xylem elements than high pressure flushing. Relative water loss (RWL) and the proportion of xylem stained with phloxine B (PSX) was also highly correlated with PLC, the latter can be quantified by image analysis, and also shows the pattern of xylem dysfunction. Loss of conductivity was more common in the inner annual rings, in early wood within an annual ring, and in compression wood, though pattern differed substantially between branches. • Advantages and potential problems of these methods are discussed and it is suggested that RWL or PSX may be used as proxy measures for PLC in species when the correlations have been established. dye staining / percent loss of hydraulic conductivity / Picea abies / relative water content / xylem embolism Résumé – Comparaison de méthodes de quantification des pertes de conductivité hydraulique chez l’épicéa