Effect Of Organ Age On Intraspecific Trait In Evergreen Coniferous Species In Northeast China

Plant functional traits play an important role in plant growth and community composition in forest ecosystem.However,how the plant intraspecific trait variations for both leaf and branch were driven by organ age is less clear.In this study,three evergreen coniferous species:Pinus koraiensis,Picea koraiensis and Abies nephrolepis in the mixed broadleaved-Korean pine(Pinus koraiensis)forest in Northeast China were used to measure the functional traits of species at different organ age in terms of morphology,stoichiometry,and hydraulic function.We used nested ANOVA coupled with variance partitioning techniques to analyze factors affecting intraspecific trait variation,linear regression models to analyze whether organ age significantly affected trait variation,principal component analysis to test for the existence of an intraspecific economic spectrum,standardized major axis analysis to screen for significant trait covariance combinations,and to test whether organ age changed this trait combination relationship.The results were as follows.(1)The specific leaf area,leaf nitrogen content,and specific branch length of Pinus koraiensis were higher than those of the other two species,and leaf dry matter content,branch dry matter content,and Huber value were lower.Among them,the coefficients of variation of specific branch length and Huber value were larger than 50%.Organ age contributed the most to the intraspecific trait variation in the three species.Additional sampled individuals explained nearly 10%of the trait variation.The sampling location(upper south and lower north)explained only less than 6%of the shape variation,indicating that canopy height had a small effect on intraspecific trait variation in the three tree species.(2)Specific leaf area,specific branch length,and leaf nitrogen content were negatively correlated with organ,and branch dry matter content was correlated with organ age,indicating that current-year branches and needles had higher specific leaf area,leaf nitrogen content,specific branch length,and lower leaf and branch dry matter content,while perennial branches and needles showed the opposite trend,and the correlation coefficients of functional traits with their organ age variation were generally low,with a maximum of only 035.In addition,the Huber values did not show correlation.(3)The results of principal component analysis of the three tree species showed that there was an intraspecific economic spectrum for the three coniferous species and that their traits show some similarity,with a trend of low specific stem length and high specific leaf area for the current year branches and the opposite trend for the perennial branches,indicating the ecological strategy of plant branches changed as the current year branches grew.We found no correlation between specific leaf area and leaf nitrogen content in the three species,which may be due to the trade-off between photosynthetic and structural nitrogen.Organ age significantly influenced the covariance among traits,suggesting that phenotypic plasticity drives trait variation rather than natural evolution.We also found that plant hydraulic traits were not influenced by organ age and did not correlate with most traits.This study highlights the important influence of organ age on plant intraspecific trait variation.The results of the study may be useful for assessing the patterns and mechanisms of plant functional trait variation and developing the global plant economic spectrum.