The Influence of Resaturation Method and Tissue 3<i>Quercus alba</i>L. Seedlings

Abstract

Parker, W. C. and Pallardy, S. G. 1987. The influence of resaturation method and tissue type on pressure-volume analysis of Quercus alba L. seedlings.—J. exp. Bot. 38: 535–549. The effect of resaturation method and amount of woody tissue on pressure-volume analysis was investigated using material collected from Quercus alba L. seedlings. Leaves excised from well-irrigated, intact plants had lower initial xylem pressure potentials than did leaves resaturated by two artificial methods. Differential capacity for tissue rehydration among the three methods was linked to shifts in the relative position of pressure-volume curves, and differences in the osmotic potential and relative water content at which turgor loss occurred were observed. Pressure-volume curves from leaves resaturated by all three methods contained ‘plateaus’ near full turgor, where xylem pressure potential declined only slightly with relative water content. These plateaus were apparently associated with apoplastic water that accumulated in intercellular spaces of the leaf near full turgidity, and acted to buffer changes in leaf xylem pressure potential as tissues dehydrated. The presence of this water has implications for derived water relations parameter estimates. Pressure-volume curves for excised shoots also exhibited plateaus, but the relationship between xylem pressure potential and relative water content over this region was steeper than was found for leaves. Shoot osmotic potentials were somewhat lower than those for leaves. The slope of the linear portion of shoot pressure-volume curves was more shallow than for single leaves, a response associated with comparatively lower values of the symplastic water fraction in shoots.