Abstract: It is generally hypothesized that tree leaves at different crown position generally adjust their structural and functional traits to achieve an optimal performance. However, it is not well understood the intra-and inter-species variation. This study investigated the foliar response of five broadleaf tree species in Northeast China to crown position (upper outer, upper inner, lower outer and lower inner). We focused on the morphological (leaf thickness), anatomical (stomatal density, guard cell length, palisade and spongy thickness) and leaf nitrogen (N) content. The results show that, there were markedly differences for the leaf traits among species or crown positions, and some strong trends were shown. Across all species, leaf and palisade thickness were both the highest at upper outer position in a crown, comparing with other locations; guard cell length and spongy thickness varied slightly within crown, but variation of leaf N content was related to species examined. Crown height and exposure degree had strong influences on leaf structure and N content variations. Among 5 species, Quercus mongolica exhibited the highest stomatal density, while the lowest guard cell length, leaf and spongy thickness, however, the reverse was Phellodendran amurrense. Our study suggests that leaves of tree species show general structure optimization in order to improve whole-tree performance.

Key words: leaf trait, anatomical structure, crown position, broadleaf tree