Effects Of Plant Size And Branch Age On Branch Traits And Relationships In Pinus Koraiensis

In order to explore the adaptation and adjustment mechanism of plants to different resources and environments,we through the study of branch traits of the main coniferous tree species in the mixed broadleaved-Korean pine(Pinus koraiensis)forest in Liangshui Nature Reserve,Heilongjiang Province,and analyzed the variation of Pinus koraiensis branches under different plant sizes,branch age and environment.Variations of many branch traits are affected by plant size,branch age and environment factors,but the relative importance of these factors to intraspecies variations of branch traits has rarely been evaluated simultaneously.In this study,we took Pinus koraiensis as the research object,to explore the effects of plant size(diameter at breast height(DBH)or tree height),branch age and environmental factors(light intensity,soil nutrient content and water availability)on branch traits and the influence of plant size(DBH or tree height),branch age and environmental factors on the trade-off between branch traits,by measuring morphological traits,chemical traits and anatomical traits in different branch ages of 69 individuals with DBH in the range of 0.3-100 cm.Our results showed that:(1)DBH and tree height had different effects on branch traits:wood density(WD),the xylem area-to-total cross-sectional area ratio(RXA),the phloem area-to-total cross-sectional area ratio(RPHA)and the pith area-to-total cross-sectional area ratio(RPA)were more sensitive to DBH,while the total resin canal area-to-total cross-sectional area ratio(RRC)and wood nitrogen content(WN)were more affected by the tree height;(2)branch age was the most important factor in driving intra-specific variations of branch traits of P.koraiensis,followed by plant size,while the impact of environment factors was minimal;(3)WD and RPHA were significantly positively correlated with DBH,while RPA was significantly negatively correlated with DBH;and RRC and WN were significantly positively correlated with tree height.Except for WN,the relationships between branch traits and branch age were significant,and as tree growth,the rate of RRC decreasing with branch age increasing was enhanced,but the rate of RPA decreasing with branch age increasing was weakened.In addition,there is a significant correlation between the traits of branch.WD is significantly positively correlated with RXA,RPHA,and tracheid density,and the correlation is gradually decreased,and there is significantly negatively correlated with RPA and RPCA,and the correlation is RPA>RPCA.There was a positive correlation between WD and RXA,RXA and RPHA,WC and WN in different plant sizes,and a negative correlation between RXA and RPCA,RXA and RPA,and RXA and tracheid density.There were significant differences in the slope of branch traits among different plant sizes.The correlation between branch traits is significantly different between branch ages.WD and RPCA,RRC,WC and WN are significantly positively correlated in different branch ages,WD is significantly negatively correlated with RXA,RXA and tracheid density.The correlation between RXA and RPA,WN and WC changes significantly with branch ages,and the correlation gradually weakens with branch age increasing.Therefore,branch age is the most important driving factor leading to intraspecies variation of branch traits in Pinus koraiensis.DBH and tree height had different effects on branch traits in different plant sizes,and current-year branch were more active than perennial branches.With the increase of DBH,the increase of WD and RPHA,the decrease of RPA,the growth rate of the plant slowed down,the photosynthetic capacity of the needles increased,the corresponding photosynthetic product transport capacity increased,and the water storage capacity of the branches weakened,which reflected the life history strategy of the branches in different life history periods.WD is significantly correlated with branch hydraulic transport(RXA)and photosynthate transport capacity(RPHA).As the plant grows,the photosynthetic capacity of needles increases,the transport capacity of water,nutrient and photosynthate of branches increases,and the wood density increases.The structure of the branch is more stable,and gradually transitions to a stable growth stage.At the plant individual level,branch traits correlated and variation law of the plant size,branch age,to determine the relations of the principal traits related regulatory mechanism for plant functional and evolutionary path prediction model building is of great significance.At the same time to predict ecosystem function and the influence of environmental change lay the foundation.