Effects Of Plant Size And Leaf Phenology On Non-structural Carbohydrates In Leaves Of Pinus Koraiensis

The non-structural carbohydrates（NSC）,including soluble sugars（SS）and insoluble starch（ST）,not only reflect the carbon supply state of plants,but also reflect the adaptation strategies of plants to the external environment.In this study,Pinus koraiensis,an established dominant species of mixed broadleaved-Korean pine forest in Liangshui National Nature Reserve of Heilongjiang Province,was selected as the research object.First,the effects of plant size（0.5-32.9 m,plant height）and environmental factors（light intensity,soil nitrogen（N）,phosphorus（P）contents and water availability）on NSC,SS and ST were investigated.Linking the differential responses of NSC,SS and ST to plant size has important implications for understanding and simulating the carbon allocation and survival patterns of plants.The results showed that Environmental factors had no significant effects on NSC,SS and ST and their dependence against needle age compared to plant height.NSC,SS and ST contents usually reached the maximum when the plant height was 25 m,which were 15.05,10.10 and 4.95 g·100 g^-1dry mass,respectively;the minimum value when the plant height was10 m,which were 8.50,5.63 and 2.88 g·100 g^-1dry mass.The NSC,SS and ST in young needles were smaller in shorter plants and the slopes of the NSC,SS and ST-needle age relationship in shorter plants were steeper.For the plant height between 0.5-10 m,the greater NSC in shorter plants was driven by lower light intensity;for the plant height between 10-25 m,the greater NSC was driven by higher plants;for the plant height>25 m,The lower NSC content in taller trees was driven by the higher soil water content.In different plant height groups,NSC increased with the increase of SS or ST,and the change slope of NSC with SS was higher than that of ST.The changes of NSC content in different plant height groups were dominated by SS,but not ST.Secondly,the influence of phenology was added to jointly explore the influence of phenology（leaf unfolding period,leafy period,leaf fall period）,life history（young,middle-aged,mature and over-mature trees;divided by plant size）and needle age（0-4year）on NSC,SS and ST and their correlation.Needle age accounted for most of the variations（42.2%-84.4%）of NSC,followed by phenology（9.2%-46.8%）,while life history accounted for only a small proportion.In general,NSC reached its maximum value during the leaf unfolding period and the shift between SS and ST occurred during the leaf fall period.The slope of NSC with phenology generally increased with increasing needle age（absolute value）.With increasing needle age,NSC and its components showed gradual upward trends.The slope of NSC with needle age decreased with leaf development（except during the leaf fall period）.Life history had significant effects on NSC,SS and ST in the leaf fall period for both current year and perennial needles,and in the leaf unfolding period only for the current year needles.Needle age significantly affected the correlations of NSC and SS（or ST）only at the leaf unfolding period.Phenology had significant effects on the correlations of NSC and SS（or ST）only for current year needle.The results clearly showed that leaf phenology and plant size could significantly affect the changes of NSC and its components.Therefore,the ecological significance of NSC and its component changes should be reconsidered by incorporating the effects of plant size and leaf phenology in future studies on leaf NSC and its component contents.