Relationship Between Leaf Nitrogen Distribution And Leaf Functional Traits Of Woody Plants In Jiangxi Province, China

Leaf Functional traits is the ecological strategy formed by plants adapting to the external living environment for a long time.It can be used as a bridge to understand the stable development of plant individual and even the whole community function.Economic spectrum of leaf（LES）refers to the trade-off between a series of interrelated and synergistic morphological,chemical and physiological functional traits of plant leaves,it may be relationship with the leaf nitrogen distribution.Leaf cell wall（structural nitrogen stock）and photosynthetic system Ribulose-1,5-bisphosphate carboxylase-oxygenase,Rubisco（photosynthetic activity nitrogen library）is the largest nitrogen pool in leaves.However,most of the studies on nitrogen distribution in LES are based on the analysis of the functional properties of the leaves at the top of the canopy in the growing season,the influence of season and canopy gradient on the functional properties of the leaves is not fully considered.Therefore,in order to investigate the seasonal variation of leaf functional traits in different canopy and its relationship with the distribution tradeoff of leaf nitrogen in structural nitrogen pool and photosynthetic active nitrogen pool.In this study,71species of woody plants（44 evergreen species,27 deciduous tree species）were selected in Yangjifeng National Nature Reserve,Jiangxi Province,Different canopy and winter and summer leaf functional traits and leaf nitrogen distribution between cell wall and Rubisco photosynthetic enzymes were measured.The main findings are as follows:（1）Mass-based photosynthetic rate(Assimilation rates per mass,A_mass)and respiration rate(Respiration rate per mass,R_mass)of upper canopy leaves were significantly higher than the lower canopy leaves in subtropical woody plants;Evergreen species Leaf mass per area（LMA）significantly higher than deciduous tree species,canopy difference significantly affected LMA of evergreen tree species.However,there was no significant effect on LMA of deciduus tree;Leaf nitrogen content(Nitrogen per mass,N_mass)and P contents(Phosphorus per mass,P_mass)in deciduous trees significantly larger than evergreen species.There was no significant crown difference between N_massand P_massof different canopy leaves.In different growing seasons,The A_mass、R_massand P_massof evergreen tree species are only significantly different in upper canopy leaves,LMA only differ in the lower canopy;N_massdid not differ significantly in different growing seasons.Summer,A_mass、R_mass、LMA、N_mass、P_massof evergreen tree species and deciduous tree species in summer.（2）Compared with winter,the trade-off relationship between key leaf functional traits of subtropical woody plants in summer is more significant.There was a significant negative correlation between LMA and A_mass、R_mass、N_mass、P_massof evergreen and deciduous trees in summer and a significant positive correlation between A_mass、R_massand N_mass、P_mass.The negative correlation between LMA and A_mass、N_mass、P_massof evergreen tree species in winter indicates that the functional traits of leaves still exist even in LES in slow growing winter.（3）Leaf mass in cell wall/Mass in leaf(M_cw/M_L)and nitrogen in cell wall（Ncw）,Nitrogen content in cell wall/Nitrogen content in leaf(N_cw/N_L),Nitrogen content in Rubisco/Nitrogen content in leaf(N_Rub/N_L)showing significant seasonal differences.M_cw/M_L、N_cw/N_L,the N_CWno significance,the N_Rub/N_Lof deciduous tree species were significantly higher than evergreen tree species in summer;A subtropical woody plant with a lower canopy leaf M_cw/M_L、N_cw、N_cw/N_L、N_Rub/N_Lhigher than the upper canopy,But there was no significant difference.Therefore,the effect of canopy gradient on nitrogen distribution in leaves was more significant than that in different growing seasons.（4）The relationship between mass based traits and leaf nitrogen distribution was stronger than that of area-based traits.There was no significant relationship between A_areaand M_cw、N_Rub/N_L、N_cw/N_Lin upper and lower canopy;Area-based respiration rate(Respiration rate per area,R_area)significantly negative correlation with N_cw/N_L、M_cw/M_Lin the upper canopy,A significant positive correlation with N_Rub/N_Lin upper and lower canopy;There was significant positive correlation between LMA and M_cw/M_L、N_CW、N_cw/N_Lin upper and lower canopy;Relationship between leaf traits and nitrogen distribution based on quality expression,A_masswas negatively correlated with M_cw/M_L、N_cw/N_L,and significantly positive correlation with N_Rub/N_Lin the lower canopy.There was a negative correlation between R_massand M_cw/M_L、N_cw/N_L,A positive correlation with N_Rub/N_Lin the upper canopy;In the upper and lower crowns,LMA and significantly negative correlation with N_CW/N_L.LMA only M_cw/M_Lsignificant positive correlation with the lower canopy.In Summary,there are seasonal and canopy differences in leaf functional traits,but these variations still accord with the LES.Growth season and life style are the main factors affecting the distribution of leaf nitrogen between leaf cell wall and Rubisco photosynthetic enzymes.The canopy gradient does not affect the distribution of leaf nitrogen.Moreover,the distribution of leaf nitrogen between cell wall（structural N library）and Rubisco photosynthetic enzymes（photosynthetic activity N library）significantly affected the functional LMA of the core leaves.