Differences In Phenotypic Plasticity In Response To Soil Moisture Between Two Invasive Plants And Their Native Congeners And The Relationships With Invasiveness

Phenotypic plasticity is one of the mechanisms first proposed to explain plant invasions.It can improve plant adaptation to stressful environment by means of changing traits in morphology,physiology,growth and reproduction.However,relationships between phenotypic plasticity and plant invasiveness are still ambiguous due to unsolved theoretical and methodological issues.Water stress is common in natural communities and water availability for plants often fluctuates.We compared differences of trait plastic responses to 4 levels of soil moisture treatment forgradient 2 seriously invasive plant species(Xanthium strumarium,Solanum rostratum)and their native congeners(X.sibiricum,S.nigrum).We measured four fitness traits(TB,RGR,FB,RA)and 18 functional traits(Biomass allocation:R:S,SBF,LBF;Morphology:LB,TLA,LAR,SLA;Water use and regulation ability in leaf:PLWP,OP,WUE;Photosynthetic assimilation:Pma.,Gs,NAR,PNUE;Pigments and element content in leaf:N,Chl,Car,C,ar/ChL).The results showed that X.strumarium can increase fitness advantages relative to native paired species by different plasticities of fitness traits whereas S.rostratum can reduced fitness disadvantages through the plasticities of fitness traits.The plasticities of LB and TLA in two invasive species are adaptive in most water gradients which can promote their successful invasions.The plasticities of OP may promote two alien speices' invasions in arid habitats as these plasticities are adaptive under low water availability.Therefore,plasticities in leaf traits may play an important role in plant invasions.Our results also showed that high Pmax and strong ability in light protection can enhance leaf carbon assimilation in both X.strumarium and S.rostratum.In addition,high PNUE in X.strumarium and high WUE in S.rostratum can improve efficiency of resource utilization,and thus promote invasion success of alien species.