Response Of Hydraulic Traits To Altitude Gradient In Different Plant Functional Types

Stomata and veins are important traits for balancing water supply and transpiration loss.Understanding the elevation pattern of stomatal and vein characteristics can reveal plant adaptation strategies to the environment and predict the response to future environment.Plant hydraulic traits(such as stomatal density and size,minor vein density)have significant differences along the environmental gradient.Although many previous studies on plant hydraulic properties have been conducted,there are few studies on how to balance various hydraulic characteristics of different plant functional types to respond to environmental changes.We measured the stomatal and vein characteristics of 96 species along the altitude gradient of 950~2656m in Taibai Mountains.By comparing the differences of hydraulic traits between different plant functional types(companion shrubs,companion trees and dominant trees),as well as their change patterns of the elevation gradient,we can deeply understand the differences of their response strategies to environmental change.The main results are as follows:1.The stomatal and vein characteristics of different plant functional types were significantly different.The dominant trees have larger stomatal density(SD),Minor vein density(MVD),node density(ND)and smaller stomatal length(SL)mean values,while the companion trees and shrubs have opposite stomatal characteristics.the mean values of sum stomatal number(SS),sum minor vein length(SMVL),sum node number(SNN)of dominant trees were significantly higher than companion trees and shrubs at leaf level.2.There were significant differences in elevation patterns of SD and SL in different PFTs.The MVD of dominant trees basically did not change with elevation,however,the SMVL of dominant trees showed a significant decreasing trend with elevation at leaf level,which indicated that the response of dominant trees to environment was mainly through changing LA rather than MVD.We also find the environmental dominant factors of different PFTs hydraulic traits are different,so we think the elevation patterns of different plant hydraulic traits are different after different pressures.Finally,the survival strategies chosen by plants to adapt to the environment after economic trade-off are revealed.3.In different plant functional types,the relationship between hydraulic characteristics is different.There was no correlation between the SD and MVD of dominant trees and companion trees,however,at leaf level,SS and SMML have a significant correlation.All of relationship between SD with MVD and SS with SMVL of companion shrubs are significant positive correlation,which proves that plants can not only coordinate the relationship between SD and MVD,but also to balance between water demand and transpiration consumption through combining with leaf size.In addition,we found that there was a coevolution relationship between MVD and ND,and there was a significant correlation between sum vein length and sum node number in different PFTs,and the difference was not significant.It is possible that the relationship between plant nodes and veins have a specific proportion.Our results show that different functional plants can adapt to environmental changes with elevation by adjusting stomatal and vein density.At the same time,the coupling relationship between stomatal and vein characteristics enables different functional plants to achieve a balance of water supply and demand at the level of leaf.This study provides more references for revealing plant adaptation strategies to the environment and predicting the response to the future environment.It also provides new evidence for the water balance hypothesis and enriches the understanding of plant response strategies to hydraulic characteristics.