The Effects of Rehydration Time on Pressure-Volume Curves of Larix gmelinii and Fraxinus mandshurica in Northeast China

Pressure-volume (P-V) curves were measured on shoots of Larix gmelinii and leaves of Fraxinus mandshurica in northeast China to analyze the effects of nonrehydrated, rehydrated, and extended rehydrated treatments on water relations parameters. For L. gmelinii, increasing rehydration time significantly increased the estimate of osmotic potential at full turgor (Ψ_π100) and at turgor loss point (Ψ_tlp) and decreased the estimate of the relative water content at turgor loss point (RWC_tlp), bulk elastic modulus (ε), and symplastic solute content per dry mass (RN_s). However, in F. mandshurica, increasing the rehydration time did not significantly change key parameters. The difference in response among these two species relates to the increase in the percent volume of apoplastic water content (AWC) in rehydrated tissues. For L. gmelinii, average AWC was 18.5% in rehydrated and 27.9% in extended rehydration treatments. For F. mandshurica, the average AWC was 4.7% in rehydrated and 4.3% in extended rehydration treatments. In contrast, the AWC value of the nonrehydrated tissue was only 0.7% for L. gmelinii and 2.7% for F. mandshurica. We recommend making P-V curves using unrehydrated tissue whenever possible to avoid potential errors caused by rehydration on the estimates of water relations parameters.