Light compensation points in shade‐grown seedlings of deciduous broadleaf tree species with different successional traits raised under elevated CO 2

We measured leaf photosynthetic traits in shade‐grown seedlings of four tree species native to northern Japan, raised under an elevated CO 2 condition, to investigate the effects of elevated CO 2 on shade tolerance of deciduous broadleaf tree species with different successional traits. We considered Betula platyphylla var. japonica and Betula maximowicziana as pioneer species, Quercus mongolica var. crispula as a mid‐successional species, and Acer mono as a climax species. The plants were grown under shade conditions (10% of full sunlight) in a CO 2 ‐regulated phytotron. Light compensation points ( LCP s) decreased in all tree species when grown under elevated CO 2 (720 μmol·mol −1 ), which were accompanied by higher apparent quantum yields but no photosynthetic down‐regulation. LCP s in Q. mongolica and A. mono grown under elevated CO 2 were lower than those in the two pioneer birch species. The LCP in Q. mongolica seedlings was not different from that of A. mono in each CO 2 treatment. However, lower dark respiration rates were observed in A. mono than in Q. mongolica , suggesting higher shade tolerance in A. mono as a climax species in relation to carbon loss at night. Thus, elevated CO 2 may have enhanced shade tolerance by lowering LCP s in all species, but the ranking of shade tolerance related to successional traits did not change among species under elevated CO 2 , i.e . the highest shade tolerance was observed in the climax species ( A. mono ), followed by a gap‐dependent species ( Q. mongolica ), while lower shade tolerance was observed in the pioneer species ( B. platyphylla and B. maximowicziana ).