Cut‐shoot vs root rehydration: Effects on pressure‐volume analysis of shoots and fascicles ofPinus resinosaseedlings

Abstract

Two methods of rehydrating red pine (Pinus resinosaAit.) shoots for pressure‐volume (PV) analysis were compared to clarify the effects of rehydration on estimated tissue water relations of shoots and fascicles. The commonly employed cut‐shoot method was compared to rehydration by means of water uptake through the roots of intact plants. Cut‐shoot rehydration and increased duration of rehydration significantly decreased estimates of tissue elasticity and relative water content at zero turgor for both shoots and fascicles. Rehydration of cut shoots for 2 days significantly increased the slope of the linear region of shoot pressure‐volume (PV) curves and decreased estimates of the apoplastic water fraction. Changes in these and estimates of other water relations attributes were correlated with increased initial water content during rehydration. Estimated apoplastic water fraction was higher for needle fascicles than shoots despite the large amount of woody stem tissue contained in shoots. Fascicle water status strongly influenced shoot water relations, in part due to apparent apoplastic loading with water of fascicles during rehydration.