Variations in leaf economics spectrum traits for an evergreen coniferous species: Tree size dominates over environment factors

Many leaf traits strongly vary with tree size and environmental factors,
but the importance of these factors to intraspecific variations of leaf
traits in forest trees have rarely been simultaneously evaluated. We
measured needle longevity and specific leaf area (SLA) and nitrogen (N)
content of every needle age (0 to 4 year old) for 65 individuals with
0.3-100 cm diameter at breast height (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
environment factors (light intensity, soil N content and water
availability) on the needle longevity, SLA, foliage N content as well as
the slopes of regressions of SLA and foliage N content against needle age.
All of the studied leaf traits and slopes of regressions of SLA and
foliage N content against needle age were significantly related to tree
size. Tree height had a greater impact on SLA and area-based leaf N
content (Narea), whereas DBH was more important for needle longevity and
mass-based leaf N content (Nmass). The environment variables, light
intensity, soil N content and water availability, were rather minor
factors for trait variations compared with tree size. Significant
influences of light intensity were found only on needle longevity, and
soil N and water availability had no effects on the leaf traits. Our study
clearly showed that tree size is an important driver of intraspecific
variations in the key leaf traits of Pinus koraiensis in a natural forest.
We also emphasize the importance of DBH or tree height varies depending on
leaf traits, suggesting various mechanisms of size effects on the
intraspecific variations in leaf traits. We suggest that ecological
significance of leaf trait variations needs reconsideration incorporating
tree size effect.