Effects Of Water Availability On The Relationships Between Hydraulic And Economic Traits Of Woody Plants In Quercus Wutaishanica Forests

Water is a vital resource for plants survival,growth and distribution.Plants adapt to different water conditions and develop corresponding water-regulation strategies involving a suite of functional traits.The response mechanism of plant communities to different water conditions,namely the hydraulics of community assembly,may be an effective perspective for the study of diversity in community ecology,reflecting the response level of plants to environmental changes different from economic traits.The present study focused on the congeneric pairs of woody species with alternative distribution,congeneric common species,and total species in Quercus wutaishanica forest which are disjunctively distributed on the Loess Plateau and Qinling Mountains（different in water availability）.This study verified the coupling relationships between hydraulic traits and economic traits and their responses along water availability to reveal the relationships between plant species turnover in water availability.It is significance to understand the water adaptation strategies of plants and the physiological and ecological mechanisms of community assembly.To clarify the reasons for the differences in species composition between the two same communities in different environments is helpful to predict the effects of climate change on species distribution and community species composition in the future.The main results are as follows:（1）There were significant differences in hydraulic traits of endemic species between the two regions,while there were no significant differences in most economic traits.The results were similar to that of congeneric common species,indicating that the differences in hydraulic traits were affected by water availability,and species on the Loess Plateau were more likely to sacrifice hydraulic efficiency to invest in hydraulic safety to adapt to the arid environment,while species in the Qinling Mountains were on the contrary.The results showed that the trade-off between hydraulic safety and hydraulic efficiency was filtering factors on species distribution and coexistence at the region scale.（2）From the perspective of congeneric common species,endemic species and total species,the correlations between hydraulic traits and economic traits were affected by water availability.Relationships were closer on the Loess Plateau with low water availability.However,there was no significant difference in the correlations between economic traits between the two regions.（3）Further studies showed that 7 pairs of correlations between economic traits and hydraulic traits(Al:As,VD and LDMC;VD and TD;WSG_branch and LMA;SD,Ψ_Tlp,VD,and P_max)and 2 pairs of correlations between hydraulic traits(Al:As and WSG_branch;SD andΨ_Tlp)changed in common species across sites,but not in endemic species.It might be a reason for common species occurrence in the two Q.wutaishanica forests with contrasting water availability.These relationships between traits may be the key to the adaptation of species.Therefore,the significant difference in species composition between the two communities was related to the change of the coupling relationships between traits.In conclusion,different combinations of hydraulic traits lead to a tradeoff between hydraulic efficiency and safety,which affects the coexistence of species at the regional scale.In the region with low water availability,relationships between hydraulic traits and economic traits,as well as between hydraulic traits are closer,and the 9 pairs of correlations between traits might be the key to determine the species composition of these two communities.The results of this study provide a scientific basis for predicting the possible response of Q.wutaishanica forests to climate change or disturbance in the future,and an important theoretical basis for vegetation conservation and restoration on the Loess Plateau and Qinling Mountains.