Effects Of Seasons And Plant Ages On Leaf Traits And Trade-offs Of Broad-leaved Species In Northeast China

Leaf economic traits showed significant variation in different seasons and different plant ages,but whether the trait variation was consistent with this variation pattern at local scale remains to be further explored;and whether the correlation between traits conforms to the global leaf economic spectrum at the local scale and whether this correlation is affected by the season and plant age remains to be tested.In this study,six broad-leaved species of broadleaved-Korean pine(Pinus koraiensis)forest:Be tula platyphylla,Ulmus japonica,Fraxinus mandshurica,Betula costata,Tilia amurensis and Acer mono selected as the study object.During the growth periods of leaf growth(June),leaf stabilization(July)and leaf senescence(September),the specific leaf area(SLA),leaf dry matter content(LDMC)and leaf thickness(LT)and mass based nitrogen content(Nmass)of adult trees and saplings were measured,and we also measured SLA,LDMC,LT and Nmass in different canopy positions for adult trees.At first,the variation of four leaf traits in different seasons,plant ages and canopy positions were analyzed;and the main factors causing variation of interspecific traits and variation of intraspecific traits in different plant sizes were also analyzed;and then we analyzed the trait-trait relationships under different resource conditions,and tested whether season and plant age have significant effects on these relationships by using Standardized Major Axis(SMA)method.The results show that:(1)There were significant variations in SLA,LDMC,LT and Nmass of all tree species in different seasons.Except for SLA of Betula platyphylla and LT of Tilia amurensis,all tree species had significant difference in SLA and LT at different plant ages,but for LDMC and Nmass,there were no significant difference at different plant ages except for LDMC of Fraxinus mandshurica and Nmass of Betula platyphylla.Under the condition of different canopy height,there was no significant difference in nitrogen content,but the other traits had significant variation.For all species as a whole,plant ages explain the major variation of SLA,and the season explains the main variation of the other three traits;for different tree species of different plant ages,the causes of intraspecies variation of traits vary with tree species and traits.(2)There was a significant correlation between the traits in different species.For the same plant age,except for SLA-Nmass for saplings,the slopes of other traits were significantly different in different seasons.For the same season,except for SLA-Nmass in leaf growth periods and LDMC-Nmass,LT-Nmass in leaf senescence periods,the slope of the correlation between the remaining traits was significantly different in different plant ages;but in the leaf stability period,only the slope of SLA-LT,LT-Nmass showed significant differences at different plant ages,the rest were not significantly different.Most traits were significantly different in different seasons and canopy positions,but only SLA and LT were significantly different in different plant ages.The influence factors of intraspecific variation were different with species and traits.For all plants of different ages at the same growth period and all plants of different growth stages at the same growth period,there was a significant correlation between most of traits,and season and plant age had significant influence on the correlation of most traits.