Variation And Tradeoff Of Leaf Traits Of Six Broadleaf Species In Mixed Broadleaved-Korean Pine Forests

There are strong interspecies differences in the leaf functional traits of plant,and the same traits of the same species behave differently in different light environments.It is of guiding significance to explore the adaptation mechanism of species with different shade tolerances based on the leaf functional traits for the selection of species in the process of plant community construction and the exploration of the species coexistence mechanism in forest community.In this study,6 broadleaf species with different shade tolerances in mixed broadleaved-Korean pine forest in northeast China were selected as study objects:Populus davidiana,Betula costata,Fraxinus mandshurica,Ulmus laciniata,Tilia amurensis and Acer mono.We measured 12 traits including leaf mass per area(LMA),leaf thickness(LT),vein density(VD),adaxial epidermis thickness(AD),palisade tissue thickness(PT),spongy tissue thickness(ST),and abaxial epidermis thickness(AB)of leaves at different canopy heights for each individual.Here,we analyzed the differences of leaf traits among species with different shade tolerances and among canopy heights from same species,and the intraspecies variation coefficient of leaf traits was explored;we revealed the relative contributions of leaf anatomical and vein traits to LMA and LT,and the direct and indirect effects of shade tolerance,mesophyll tissue thickness and VD on LMA were explored;we also analyzed the relationships between leaf traits,and the allometric relationship among leaf traits and the difference among species with different shade tolerances were explored.The results showed that:(1)Leaf traits were significantly different among species with different shade tolerances,on the whole,shade-intolerant species had higher LMA,PT,VD,and shade-tolerant species had higher AD and AB,the PT/ST of shade-intolerant species was greater than 1,while that of shade-tolerant species was less than 1.Leaf traits were significantly different among the different canopy heights,the LMA,LT,PT and ST of the upper leaves were significantly higher than those of the lower leaves,the proportion of adaxial epidermis(ADP)and the proportion of abaxial epidermis(ABP)of the upper leaves were significantly lower than those of the lower leaves.For each species,LMA,PT,ST and PT/ST had higher intraspecific variation coefficients,while the proportion of palisade tissue(PTP)and the proportion of spongy tissue(STP)had lower intraspecific variation coefficients.(2)LT and LMA could be explained by leaf anatomical and vein traits,the relative contributions of PT and ST were greater for the variation of LT and LMA,the relative contribution of VD to LT was less than that of AD and AB,while the relative contribution of VD to LMA was greater than that of AD and AB.Shade tolerance of species had a significant negative direct effect on LMA,and could indirectly affect LMA by affecting PT,ST and VD.(3)There were extremely significant relationships between leaf traits.There were allometric relationships among leaf traits,and the allometric growth index was different among different species.For most study species,there were positive allometric relationships among LT,PT and ST,and PT had the fastest growth rate,while LT had the slowest growth rate.LMA had the same growth rate with LT and ST,there was a positive allometric relationship between LMA and PT.In conclusion,leaf functional traits were closely related to shade tolerance of species,the study on the variation and tradeoff of leaf traits of specie with different shade tolerances was conducive to the further analysis of resource acquisition strategies and light adaptation mechanisms of species with different shade tolerances.The results verified and supplemented the previous studies,and suggest that the shade tolerance of species should be taken into account in the study on interspecific differences of leaf traits and the study on the allometric relationships among leaf traits,and the vertical distribution within a canopy of leaf traits should be considered in the study on intraspecies variation of leaf traits.