Variation And Trade-off Of Twig And Leaf Traits Of Korean Pine At Different Time Scales

Plant functional traits are the comprehensive reflection of the plant adapting to environmental changes during the long evolution and development process.As an important part of plant organs,twigs play an important role in water transport,reserve of nutrients and mechanical support for leaves.In addition,the relationship between twig-leaf size and volume-based leafing intensity reflects the ability of plants to utilize space resources.In Liangshui National Nature Reserve,Heilongjiang Province,the Pinus koraiensis as the main dominant species of mixed broadleaved-Korean pine forest were selected.Through the analysis of the different phenological stages（leaf extension period,leaf fullness period and leaf senescence period）,different life-history stages（seedlings,saplings,adult trees,old trees）and twig ages（0-3 years）of twig traits and leaf traits.To explore the variation of twig traits in different phenological stages and twig ages,the effects of phenology and twig ages on the cooperative relationship between twig traits;and the variation and trade-offs of twig and leaf traits at different life history stages.We found that the phenological periods can significantly affect the twig wood density（TWD）,twig dry matter content（TDMC）,xylem area-to-total cross-sectional area ratio(R_XA)and Total resin canal area-to-total cross-sectional area ratio(R_RC).Twig at leaf extension period had low TDMC and TWD,twigs at leaf fullness period had high R_XA,and twigs at leaf senescence period usually had high R_RC.Our results showed that current year twigs have high specific twig length（STL）and R_RC,low TDMC,TWD and R_XA,while perennial twigs showed the opposite trend.Twigs at different phenological periods and twig ages had different resource trade-off strategies.And there were significant correlations between most twig traits.Twig age changed the most of the trait-trait relationships,while the relationships between twig traits in different phenology periods most existed only in a certain phenological period.This suggested that twig age was an important factor driving variation among traits,while the degree of development of twigs at different phenological periods influenced the trade-off relationship among traits.The twig cross-sectional area（TCA）and leaf area（TLA,ILA）increased with the gradient of life history stages,while the leafing intensity（LIV）decreased.There were significant differences in twig and leaf traits among leaf and twig ages.Leaf and twig ages accounted for the most of the variations in leaf and twig traits.Life history stages accounted for 17%,7%and 3%of the total variation of TCA,TLA and ILA.The correlation between current year twig and leaf traits at different life history stages of Korean pine showed heterotrophic growth.There was a positive correlation between TCA and TLA at the seedling stage and old tree stage.At the seedling stage,there was a positive correlation between TCA and ILA and a negative correlation between LIV and ILA.There was a negative correlation between TCA and LIV at seedling,adult and old tree stages.As for the correlation between TCA and TLA,TCA and LIV at different twig ages at different life history stages,it was found that the TCA and TLA of the current-year twigs at the seedling and old tree stages were positively correlated.And at sapling,adult and old tree stage,there was a positive correlation between TCA and TLA in 1-year-old twig,and a negative correlation between TCA and LIV in current-years twigs,a negative correlation both 1-year-old and 2-year-old twigs at the old tree stage.Twigs at different phenological stages,different life history stages and different twig ages of Korean pine have different resource utilization strategies.By exploring the variation and collaborative relationship of twig and leaf traits at different levels,we have deepened our understanding of the self-regulation mechanism of conifers and their responses to environmental changes,which are of great significance for understanding branch traits of conifers at the local level.