Differential anatomical responses to elevated CO2 in saplings of four hardwood species


T. Koike. Fax: +81 11 706 2517; e-mail: tkoike@for.agr.hokudai.ac.jp


To determine whether an elevated carbon dioxide concentration ([CO2]) can induce changes in the wood structure and stem radial growth in forest trees, we investigated the anatomical features of conduit cells and cambial activity in 4-year-old saplings of four deciduous broadleaved tree species – two ring-porous (Quercus mongolica and Kalopanax septemlobus) and two diffuse-porous species (Betula maximowicziana and Acer mono) – grown for three growing seasons in a free-air CO2 enrichment system. Elevated [CO2] had no effects on vessels, growth and physiological traits of Q. mongolica, whereas tree height, photosynthesis and vessel area tended to increase in K. septemlobus. No effects of [CO2] on growth, physiological traits and vessels were seen in the two diffuse-porous woods. Elevated [CO2] increased larger vessels in all species, except B. maximowicziana and number of cambial cells in two ring-porous species. Our results showed that the vessel anatomy and radial stem growth of Q. mongolica, B. maximowicziana and A. mono were not affected by elevated [CO2], although vessel size frequency and cambial activity in Q. mongolica were altered. In contrast, changes in vessel anatomy and cambial activity were induced by elevated [CO2] in K. septemlobus. The different responses to elevated [CO2] suggest that the sensitivity of forest trees to CO2 is species dependent.