A Study On The Leaf Economic Traits And Hydraulic Traits Of Woody Plants On The Loess Plateau

Plant functional traits are a series of morphological,structural and physiological characteristics that have great effects on the growth,propagation and survival of plants.Trait-based approaches are helping to deepen our understanding of the mechanisms that drive species coexistence,community assembly and successional dynamics.Among various traits,those related to light capture and carbon economy,such as maximum net photosynthesis rate,leaf life span,leaf dry mass per area and leaf nitrogen concentration,form the leaf economic traits.On the other hand,those related to water demand and supply form the hydraulic traits,such as vein density,leaf hydraulic conductance,stomatal density and stomatal size.Water transport and CO₂ diffusion are two important processes that determine the CO₂ assimilation efficiency in leaves.Therefore,the integration of economic traits and hydraulic traits will help to present a more comprehensive view of the acclimation of plants.This study was focused on the traits of woody plants on the Loess Plateau,combining with community succession and biomass allocation.The main conclusions are as follows:?1?Plants on the Loess Plateau had significantly higher leaf nitrogen concentration per mass,leaf nitrogen concentration per area,leaf tissue density,and vein density compared to those from tropical-subtropical regions.Plants from tropical-subtropical regions had significantly higher leaf thickness,stomatal length and maximum stomatal conductance to water vapour than those of the Loess Plateau.Leaf dry mass per area and stomatal density showed no significant differences between the Loess Plateau and tropical-subtropical regions.These differences of traits between the two regions are helping for plants to acclimate to the arid environment of the Loess Plateau.Economic traits and hydraulic traits are coupled on the Loess Plateau which is converse to the result in tropical-subtropical regions.The relationships of these two sets of traits may depend on water availability.?2?Leaf hydraulic conductance showed no significant correlations with water potential at 50%loss of hydraulic conductance,showing the lack of trade-off between hydraulic efficiency and draught vulnerability.This lack of trade-off may be beneficial for plants in arid regions.On this precondition,plants with a high hydraulic efficieny could keep a low draught vulnerability to prevent from xylem embolism,while could also keep a high draught vulnerability to prevent from extreme drought by leaf shedding.?3?Among economic traits,plants in pioneer trees stage had significantly higher maximum net photosynthesis rate compared to those from shrub stage and climax tree stage on average.Other economic traits showed no significant difference among three successional stages.Among hydraulic traits,species from pioneer tree stage showed significantly higher vein density and stomatal length than climax tree stage.Leaf area to sapwood area ratio of plants showed a significantly increasing pattern in the order of shrub stage,pioneer tree stage to climax tree stage.In addition,leaf water potential at turgor loss point and maximum stomatal conductance to water vapour showed no significant difference among three successional stages.Species from pioneer tree stage exhibited"fast-growing"characteristics so that they could win the competition with shrubs.But pioneer tree species have low survival rates and die quickly in shade environment.On the contrary,species from late successional stage exhibited"slow-growing"characteristics,but they had high survival rates in shade environment.Therefore,late successional trees win the competition with pioneer trees after the slow growth for a long time.?4?As two important indicators that exhibit biomass allocation of plants,leaf mass fraction and leaf area ratio show significant positive correlation in the present study.But they play different roles in the acclimation of plants.Leaf mass fraction is mainly related to drought tolerance while leaf area ratio is mainly related to light capture.After all,hydraulic traits play importent roles in the community succession and biomass allocation of woody plants on the Loess Plateau.Studies on plant hydraulic traits should be strengthened in the future work.Hydraulic traits are coupled with economic traits.The integration of economic traits and hydraulic traits will deepen our understanding on the succession and biomass allocation of woody plants.This study will provide theoretical foundation for guiding vegetation restoration and reconstruction of the Loess Plateau.