Light Compensation Points In Shade-Grown Seedlings Of Deciduous Broadleaf Tree Species With Different Successional Traits Raised Under Elevated Co2

Abstract

We measured leaf photosynthetic traits in shade￢ﾀﾐgrown seedlings of four tree species native to northern Japan, raised under an elevated CO2 condition, to investigate the effects of elevated CO2 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￢ﾀﾐsuccessional species, and Acer mono as a climax species. The plants were grown under shade conditions (10% of full sunlight) in a CO2￢ﾀﾐregulated phytotron. Light compensation points (LCPs) decreased in all tree species when grown under elevated CO2 (720ￂﾠￎﾼmolￂﾷmol￢ﾈﾒ1), which were accompanied by higher apparent quantum yields but no photosynthetic down￢ﾀﾐregulation. LCPs in Q.ￂﾠmongolica and A.ￂﾠmono grown under elevated CO2 were lower than those in the two pioneer birch species. The LCP in Q.ￂﾠmongolica seedlings was not different from that of A.ￂﾠmono in each CO2 treatment. However, lower dark respiration rates were observed in A.ￂﾠmono than in Q.ￂﾠmongolica, suggesting higher shade tolerance in A.ￂﾠmono as a climax species in relation to carbon loss at night. Thus, elevated CO2 may have enhanced shade tolerance by lowering LCPs in all species, but the ranking of shade tolerance related to successional traits did not change among species under elevated CO2, i.e. the highest shade tolerance was observed in the climax species (A.ￂﾠmono), followed by a gap￢ﾀﾐdependent species (Q.ￂﾠmongolica), while lower shade tolerance was observed in the pioneer species (B.ￂﾠplatyphylla and B.ￂﾠmaximowicziana).