The Effects Of Rehydration Time On Pressure-Volume Curves Of The Major Tree Species In The Eastern Mountain Region Of Northeast China

Severe droughts have been associated with regional-scale forests mortality worldwide.The pressure-volume(P-V)technique is frequently used to estimate various leaf water relations parameters.P-V curve analysis has greatly enlarged our understanding of plant water relations,as well as our knowledge of the functional significance of adaptive modifications of key parameters under drought stress conditions.Although P-V analysis has undergone several improvements in the last several decades,questions remain regarding whether experimental material should be rehydrated artificially or not and whether the length of the rehydration time affects the results.In this study,we analyzed the effects of rehydration time(nonrehydrated,rehydrated 12 h,and extended rehydration 24 h treatments)on the water relations parameters estimated from P-V curves using Larix gmelinii(Rupr.)Kuzen,Picea koraiensis Nakai.,Pinus koraiensis Sieb.,Phellodendron amurense Rupr.,Fraxinus mandshurica Rupr.,Juglans mandshurica Maxim.,Quercus mongolica Fisch.ex Turcz.,Acer mono Maxim.,Betula platyphylla Suk.,main tree species in northeast China.For L.gmelinii,P aspeata,and P.koraiensis,increasing rehydration time increased the estimate of osmotic potential at full turgor(ψsat)and at turgor loss point(ψtlp)and decreased the estimate of the relative water content at turgor loss point(RWtlp),percent volume of apoplastic water content(AWC),bulk elastic modulus(εmax),and symplastic solute content(Ns).For B.platyphylla,Q.mo golica,and A.mono,increasing rehydration time increased the estimate of ψsat and ψtlp and decreased the estimate of the RWCtlp,AWC,and εmax,and unconsistent trend for Ns among different treatments.The different rehydration treatments did not affect any of the other water relations parameters significantly(P>0.05).In general,in F.mandshurica,P.amurense,J.mandshurica increasing the rehydration time did not significantly change key parameters such as ψsat,ψtlp,RWCtlp,and AWC whereas variation of εmaxand Ns for rehydration and extended rehydration was in the range of 1%-86%coMPared with the nonrehydration treatment.Increasing the amount of leaflet from 3 leaflet,5 leaflet,to 7 leaflet increased the estimate of ψsat,ψtlp,RWCtip,and AWC whereas patterns forεmax and Ns showed unconsistent.Water parameters comparison among nine tree species in rehydration,and extended rehydration had changed significantly,with the exception of AWC in rehydration treatment compared to nonrehydration.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.