Plastic changes of leaf mass per area and leaf nitrogen content in response to canopy openings in saplings of eight deciduous broad-leaved tree species

Leaf nitrogen content per area (N-area) is a good indicator of assimilative capacity of leaves of deciduous broad-leaved trees. This study examined the degrees of increase in Narea in response to canopy openings as leaf mass per area (LMA) and leaf nitrogen content per mass (N-mass) in saplings of eight deciduous broad-leaved tree species in Hokkaido, northern Japan. Five of the species were well-branched species with a large number of small leaves (lateral-growth type), and the other three species were less-branched species with a small number of large leaves (vertical-growth type). The degrees of increase in Narea were compared between the two crown types. In closed-canopy conditions, leaves of the vertical-growth species tended to have a lower LMA and higher N-mass than those of the lateral-growth species, which resulted in similar N-area for both. LMA increased in canopy openings in the eight species, and the degrees of increase were not largely different between the lateral- and vertical-growth species. On the contrary, N-mass was unchanged in canopy openings in the eight species. As a result, N-area of each species increased in canopy openings in proportion to the increase in LMA, and the degrees of increase in N-area were similar in the lateral- and vertical-growth species. Therefore, this study showed that the degrees of increase in N-area were not correlated with the crown architecture (i.e., the lateral- and vertical-growth types).