A comparison of the composite and repeat pressurization methods of pressure–volume analysis for shoots of four North American conifer species

Significantly different water relations attributes were derived for temperate conifers measured using the repeat pressurization (RP) and composite (CM) pressure–volume (PV) procedures. In the RP method, single shoots were measured 10–20 times for xylem water potential and mass during air-drying to produce each PV curve. In contrast, for CM PV curves 25–30 shoots were air-dried to relative water contents (R) ranging from 1.0 to 0.5 before being pressurized once. Aggregation of these 25–30 paired values produced single PV curves. Pinus banksiana, P. resinosa and Picea mariana, but not Pinus strobus, had lower full turgor osmotic potential, shallower slope of the linear segment of the PV curves and higher symplast fraction with the CM method. Data points along the linear segment of PV curves were obtained to lower R using the CM method. Reanalysis using similar R ranges eliminated differences between PV methods for Picea mariana but not Pinus banksiana and P. resinosa.