Evaluation of centrifugal methods for measuring xylem cavitation in conifers, diffuse- and ring-porous angiosperms

Abstract

• A centrifugal method is used to measure 'vulnerability curves' which show the loss of hydraulic conductivity in xylem by cavitation. Until recently, conductivity was measured between bouts of centrifugation using a gravity-induced head. Now, conductivity can be measured during centrifugation. This 'spin' method is faster than the 'gravity' technique, but correspondence between the two has not been evaluated. • The two methods were compared on the same stem segments for two conifer, four diffuse-porous, and four ring-porous species. • Only 17 of 60 conductivity measurements differed, with differences in the order of 10%. When different, the spin method gave higher conductivities at the beginning of the curve and lower at the end. Pressure at 50% loss of conductivity, and mean cavitation pressure, were the same in 14 of 20 comparisons. When different, the spin method averaged 0.32 MPa less negative. Ring-porous species showed a precipitous initial drop in conductivity by both techniques. This striking pattern was confirmed by the air-injection method and native embolism measurements. • Close correspondence inspires confidence in both methods, each of which has unique advantages. The observation that ring-porous species operate at only a fraction of their potential conductivity at midday demands further study. © The Authors (2007).