Zhili Liu, Kouki Hikosaka, Fengri Li, Guangze Jin

Many leaf traits strongly vary with tree size and environmental factors, but their relative contributions to leaf trait variation in forest trees have rarely been simultaneously evaluated. Additionally, diameter at breast height (DBH) and tree height are often used to quantify tree size, but whether the influence of DBH and tree height on leaf trait variation differs between traits has rarely been examined.   

We here measured needle longevity, specific leaf area (SLA, leaf area per unit mass) and nitrogen (N) content of every needle age (0 to 4 years old) for 65 individuals with 0.3-100 cm DBH for an evergreen coniferous species, Pinus koraiensis Sieb. et Zucc., in Northeast China. We simultaneously evaluated effects of tree size (DBH or tree height) and environmental factors (light intensity, soil N content and water availability) on needle longevity, SLA and foliage N content, as well as the relationships between SLA, foliage N content and needle age.

We found that all of the studied leaf traits and relationships of SLA , and foliage N content with needle age were significantly related to tree size. Tree height had a greater impact on SLA and area-based leaf N content, whereas DBH was more important for needle longevity and mass-based leaf N content (Nmass). Light intensity, soil N content and water availability had rather minor effects on trait variation compared with tree size. Significant influences of light intensity were found only on needle longevity and Nmass, and soil N and water availability had no effect on leaf traits.

Our study clearly showed that tree size is an important driver of intraspecific variation in the key leaf traits of Pinus koraiensis in a natural forest. We also emphasize that the importance of DBH or tree height varies depending on leaf traits, suggesting that the size effect operates via various mechanisms. We suggest that the ecological significance of leaf trait variatios needs reconsideration, bearing in mind the role of tree size.

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