We set up a free-air ozone (O 3 ) exposure system for determining the photosynthetic responses of Siebold's beech (Fagus crenata) and oak (Quercus mongolica var. crispula) to O 3 under field conditions. Ten-year-old saplings of beech and oak were exposed to an elevated O 3 concentration (60 nmol mol -1 ) during daytime from 6 August to 11 November 2011. Ozone significantly reduced the net photosynthetic rate in leaves of both species in October, by 46% for beech and 15% for oak. In beech there were significant decreases in maximum rate of carboxylation, maximum rate of electron transport in photosynthesis, nitrogen content and photosynthetic nitrogen use efficiency, but not in oak. Stomatal limitation of photosynthesis was unaffected by O 3 . We therefore concluded photosynthesis in beech is more sensitive to O 3 than that in oak, and the O 3 -induced reduction of photosynthetic activity in beech was due not to stomatal closure, but to biochemical limitation. Capsule:Photosynthesis of beech is more sensitive to free air ozone exposure than that of oak

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.

Betula platyphylla var. japonica (white birch) has heterophyllous leaves (i.e., early and late leaves) and is a typical pioneer tree species in northern Japan. Seedlings of white birch were exposed to ozone during two growing seasons, and measurements were carried out in the second year. Early leaves did not show an ozone-induced reduction in photosynthesis because of lower stomatal conductance resulting in higher avoidance capacity for ozone-induced stress. Also, an ozone-related increase in leaf nitrogen content may partly contribute to maintain the photosynthetic capacity in early leaves under elevated ozone in autumn. On the other hand, late leaves showed an ozone-induced decline of photosynthesis and early defoliation of leaves occurred. Also, smaller leaf size and higher stomatal density in late leaves were observed under elevated ozone. Differences in stress resistance to ozone may be related to differing functional roles of early and late leaves for birch species.

With the rapid industrial development and modern agricultural practices, increasing nitrogen (N) deposition can cause nutrient imbalance in immature volcanic ash soil commonly found in Japan. Larch species, widely distributed in northeast Eurasia, are associated with ectomycorrhizal (ECM) fungi which play a critical role in nutrient acquisition for their hosts. In this study, we investigated species richness and diversity of ECM fungi associated with a hybrid larch (F) and its parents, Dahurian larch (Larix gmelinii var. japonica) and Japanese larch (L. kaempferi), under simulated N deposition (0 and 100kghayr) with/without phosphorous (P) (0 and 50kghayr). Seedlings planted in immature volcanic ash with low nutrient availability were subjected to the N and P treatments for fifteen months. We found that response of ECM community structure to the increased nutrient availability depended on host genotypes. Nutrient addition significantly affected ECM structure in Japanese larch, but no such significant effect was found for Dahurian larch. Effects of the nutrient addition to ECM fungal community in F were intermediate. F was tolerant to high N loading, which was due to consistent, relatively high association with Suillus sp. and Hebeloma sp. F showed heterosis in relative biomass, which was most apparent under high N treatments. This co-variation of ECM fungal community structure and F biomass in response to N loading suggest that ECM community structure might play an important role in host growth. The present findings indicate effects of N deposition on ECM fungal community structure can depend on larch species, thus it is challenging to predict general trends.