Norikazu Eguchi

Changes in Morphology, Anatomy, and Photosynthetic Capacity of Needles of Japanese Larch (Larix kaempferi) Seedlings Grown in High CO2 Concentrations

Photosynthetic traits of two-year-old Japanese larch seedlings (Larix kaempferi Carr.) grown at elevated CO2 concentrations were studied in relation to structural changes in the needles. Seedlings were grown at two CO2 concentrations, 360 (AC) and 720 (EC) μmol mol−1 at high and low nutrient supply rates, high N (HN) and low N (LN). The photosynthetic capacity fell significantly in EC+LN, but increased significantly in EC+HN. Since the mesophyll surface area exposed to intercellular space per unit leaf area (Ames/A) is correlated with the photosynthetic rate, we measured Ames/A for larch needles growing in EC. Changes of Ames/A in both EC+HN and EC+LN were very similar to the changes in photosynthetic capacity. This suggests that the changes of Ames/A in EC probably caused the changes in the photosynthetic capacity. The changes of Ames/A in EC were attributed to changes in the mesophyll cell size and mesophyll cell number. The photosynthetic capacity in EC can be explained by taking morphological and structural adaptations into account as well as biochemical factors.

Light compensation points in shade-grown seedlings of deciduous broadleaf tree species with different successional traits raised under elevated CO2.

We measured leaf photosynthetic traits in shade-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-successional species, and Acer mono as a climax species. The plants were grown under shade conditions (10% of full sunlight) in a CO2 -regulated phytotron. Light compensation points (LCPs) decreased in all tree species when grown under elevated CO2 (720 μmol·mol(-1) ), which were accompanied by higher apparent quantum yields but no photosynthetic down-regulation. LCPs in Q. mongolica and A. mono grown under elevated CO2 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 CO2 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 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. mono), followed by a gap-dependent species (Q. mongolica), while lower shade tolerance was observed in the pioneer species (B. platyphylla and B. maximowicziana).

Effects of Elevated CO2 on Ecophysiological Responses of Larch Species Native to Northeast Eurasia

Larch species are broadly distributed in the northern hemisphere, and dominate the landscape especially in the northeastern part of the Eurasian continent where permafrost is well developed (Abaimov et al. 1998, 2000; Kajimoto et al. 2003, 2006). Four species of larch, Larix sibirica, L. gmelinii, L. cajanderi, and L. kaempferi, predominate in the eastern Eurasia (Koike et al. 2000a; see Chap. 3). Taxonomy of Larix is still somewhat unsettled in the eastern half of Siberia, and particularly in the Far East of the Russian Federation. Although Larix in the latter region was not generally classified as L. gmelinii in Russia (Abaimov et al. 1998), the larches native to Sakhalin and Kuril Islands have customarily been referred to as L. gmelinii by some workers (Kurahashi 1988; Uemura et al. 1994; LePage and Basinger 1995; see also Chap. 3). Therefore, we describe the Larix species from Sakhalin and Kuril Islands, and that transplanted in Hokkaido, northern Japan, as L. gmelinii hereafter in this chapter.

Photosynthetic traits of Siebold's beech seedlings in changing light conditions by removal of shading trees under elevated CO2

The purpose of this study was to obtain basic information on acclimation capacity of photosynthesis in Siebolds beech seedlings to increasing light intensity under future elevated CO2 conditions. We monitored leaf photosynthetic traits of these seedlings in changing light conditions (before removal of shade trees, the year after removal of shade trees and after acclimation to open conditions) in a 10-year free air CO2 enrichment experiment in northern Japan. Elevated CO2 did not affect photosynthetic traits such as leaf mass per area, nitrogen content and biochemical photosynthetic capacity of chloroplasts (i.e. maximum rate of carboxylation and maximum rate of electron transport) before removal of the shade trees and after acclimation to open conditions; in fact, a higher net photosynthetic rate was maintained under elevated CO2 . However, in the year after removal of the shade trees, there was no increase in photosynthesis rate under elevated CO2 conditions. This was not due to photoinhibition. In ambient CO2 conditions, leaf mass per area and nitrogen content were higher in the year after removal of shade trees than before, whereas there was no increase under elevated CO2 conditions. These results indicate that elevated CO2 delays the acclimation of photosynthetic traits of Siebolds beech seedlings to increasing light intensity.

Photosynthetic and Photosynthesis-Related Responses of Japanese Native Trees to CO2: Results from Phytotrons, Open-Top Chambers, Natural CO2 Springs, and Free-Air CO2 Enrichment

We explore the effects of elevated CO2, in relation to other environmental factors, on leaf photosynthesis, the functioning of other organs, and the plant as a unit, primarily in tree species and herbs common to cool temperate forests in northeast Asia. First, results of a series of chlorophyll fluorescence and gas exchange studies using white birch as a model tree species are discussed. Excess energy appears to be suppressed by enhancing photosynthetic capacity or thermal dissipation, depending on the availability of nitrogen in both current and elevated CO2 levels. Next, evidence suggests adaptation of wild plants to CO2 near springs. If some adaptation occurs, plants will not necessarily respond like current plants to future environmental change. Finally, physiological ecology of woody plants grown in open top chambers and Free-Air CO2 Enrichment (FACE) is summarized in relation to the changing environment. This summary emphasizes that effects of future environments on plants should be examined by paying attention not only to CO2 but also to various environmental components, such as soil types, nutrient availability, herbivores, mycorrhizae, ground level O3, and methane emission.