We studied the colonization of ectomycorrhizal fungi and species abundance of a hybrid larch (F1) under elevated CO₂ and O₃. Two-year-old seedlings were planted in an Open-Top-Chamber system with treatments: Control (O3 < 6 nmol/mol), O₃ (60 nmol/mol), CO₂ (600 μmol/mol), and CO2 + O₃. After two growing seasons, ectomycorrhiza (ECM) colonization and root biomass increased under elevated CO₂. Additionally, O₃ impaired ECM colonization and species richness, and reduced stem biomass. However, there was no clear inhibition of photosynthetic capacity by O₃. Concentrations of Al, Fe, Mo, and P in needles were reduced by O₃, while K and Mg in the roots increased. This might explain the distinct change in ECM colonization rate and diversity. No effects of combined fumigation were observed in any parameters except the P concentration in needles. The tolerance of F1 to O₃ might potentially be related to a shift in ECM community structure.

We studied the effects of elevated ozone ([O 3 ]) and CO 2 concentrations ([CO 2 ]) on the growth and photosynthesis of the hybrid larch F 1 (F 1 ) and on its parents (the Dahurian larch and Japanese larch). F 1 is a promising species for timber production in northeast Asia. Seedlings of the three species were grown in 16 open top chambers and were exposed to two levels of O 3 (⁄10 ppb and 60 ppb for 7 h per day) in combination with two levels of CO 2 (ambient and 600 ppm for daytime) over an entire growing season. Ozone reduced the growth as measured by height and diameter, and reduced the needle dry mass and net photosynthetic rate of F 1 , but had almost no effect on the Dahurian larch or Japanese larch. There was a significant increase in whole-plant dry mass induced by elevated [CO 2 ] in F 1 but not in the other two species. Photosynthetic acclimation to elevated [CO 2 ] was observed in all species. The net photosynthetic rate measured at the growing [CO 2 ] (i.e. 380 ppm for ambient treatment and 600 ppm for elevated CO 2 treatment) was nevertheless greater in the seedlings of all species grown at elevated [CO 2 ]. The high [CO 2 ] partly compensated for the reduction of stem diameter growth of F 1 at high [O 3 ]; no similar trend was found in the other growth and photosynthetic parameters, or in the other species.

The effects on birch (Betula spp.) of elevated carbon dioxide (CO 2 ) and ozone (O 3 ), which are both increasing in the troposphere, are surveyed in detail based on the literature. Birches establish themselves in the open field after disturbances, and then become dominant trees in temperate or boreal forests. Ecophysiological approaches include the measurement of photosynthesis, biomass, growth, and survival of seedlings and trees. Elevated CO 2 levels give rise to a net enhancement of the growth of birch trees, whereas high O 3 generally reduces growth. Although the effects of the two are opposed, there is also an interactive effect. Basic physiological responses of the single genus Betula to CO 2 and O 3 are set out, and some data are summarized regarding ecological interactions between trees, or between trees and other organisms.