Delaying drought-driven leaf cells damages may be the key trait of invasive trees ensuring their success in the Mediterranean basin

nvasivealienspecies(IAS)threatenthebiodiversityrichnessoftheMediterraneanbasin,adrought-proneregion.However,ourknowledgeontheadaptivestrategiesofIASforfacingMediterraneandroughtsummersisstillincomplete.Theaimofthepresentstudyistocomparethewaterrelationsandthecriticalrelativewatercontent(RWC)valuesleadingtolossofcellrehydrationcapacityoftwoMediterraneanbasinIAS(i.e.,Ailanthusaltissima(Mill.)SwingleandRobiniapseudoacaciaL.)versustwoco-occurringnativespecies(i.e.,FraxinusornusL.andQuercuspubescensWilld.).StudyIASshowedhighervaluesofwaterpotentialatturgorlosspointandosmoticpotentialatfullturgor,lowervaluesofmodulusofelasticityandleafmassareabuthigherphotosynthesisrate,evenduringthesummer,withrespecttotheMediterraneannativespecies.ThesefindingssupportedthehypothesisthatIASarecharacterizedbyaresourceacquisitivestrategycoupledwithasafety-efficiencytrade-off,comparedwithMediterraneannativespecies.However,similarleafRWCthresholdsleadingtolossofcellrehydrationcapacitywererecordedinthetwogroupsofspecies.Moreover,IASshowedhighersaturatedwatercontentandcapacitancevaluescomparedwiththeco-occurringspecies.Overall,ourresultssuggestthatthesuccessofMediterraneanIASisdrivenbytheirabilitytodelaydehydrationdamageofmesophyllcellsduringMediterraneansummerdrought,therebysupportingtheirdistinctivehighcarbonassimilationrate.