|Budget Amount *help
¥3,600,000 (Direct Cost : ¥3,600,000)
Fiscal Year 1999 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥2,600,000 (Direct Cost : ¥2,600,000)
Increases in solar UV-B (ultraviolet-B radiation, here taken as 290-315 nm) are expected to result from stratospheric ozone depletion. In this study, the effects of UV-B on physiological responses in forest tree species were examined. We constructed novel UV-B radiation system, which can control the dose of supplemental UV-B in proportion to ambient UV-B. The level of UV-B enhancement was up to 1.3 times that in ambient UV-B. The photosynthetic capacities, such gas exchanges and PS II photochemical efficiency, the composition of photosynthetic pigments and UV-B absorbing compound, the activities of the enzymes in the active oxygen-scavenging system were also examined.
Because forest trees are exposed to UV-B radiation on long term basis, the increase of UV-B are likely affected to the productivity in artificial forests and species composition in natural forests.
Sugi (Cryptomeria japonica)is one of the most important coniferous species in Japan. The area of sugi plantations occupies appr
oximately 45% of all the artificial forest. In order to assess the affect of the increased UV-B in the productivity of artificial forest, we designed three levels in UV-B radiation in the nursery. Those were, enhanced UV-B treatments using an UV-B radiation system different, decreased level of UV-B using the UV-cutting films, and ambient level of UV-B. The physiological responses of sugi saplings were examined. While the sugi saplings grown in the decreased UV-B level showed slightly increasing in the photosynthetic rate and PS II photochemical efficiency (Fv/Fm), no significant changes were observed between the saplings in the enhanced UV-B and that in the ambient UV-B.
In order to understand the influence of the increased UV-B on the species composition in natural forest, we investigate the physiological responses of the five tree species grown in the natural beech (Fagus crenata) forest Mt. Naeba-san. The five species were treated with different UV-B levels using UV-B cutting films. In addition, the seedlings grown in the naturally occurred different UV-B levels were also examined. While the beech seedlings grown in the decreased UV-B level showed significant decrease in the UV-B absorbing compounds compared with that in the ambient level, the seedlings exposed the strong light, which may include high level of UV-B, showed the increase in the UV-B absorbing pigments. Some changes were observed in the chlorophyll contents, chlorophyll a/b ratio, and the pool size of xanthophyll cycle pigments. Since the preliminary experiment using the growth chambers equipped with UV-B radiation system showed the rapid accumulation of the UV-B absorbing pigments in the beech seedlings, the difference observed in the UV-B absorbing pigments was attributed to be adaptation to the UV-B levels where the seedlings were growing. Therefore, beech seedlings growing in the field seemed to have the abilities to accumulate the UV-absorbing pigments in response to the UV-B levels. However, the differences in the timing of the leaf senescence were observed in the seedlings treated with different UV-B levels. Timing of the leaf senescence was earlier in the seedlings treated with high UV-B level. Although the maximum PS II photochemical efficiency were not significantly changed among the five species, the maximum amount of UV-B absorbing pigments were observed. While the differences in the PS II photochemical efficiency between the different UV-B levels within species were not significantly changed among the five species, differences in the range, of the amounts of UV-absorbing pigments between the different UV-B levels within species were observed.
These results suggest that the forest tree species have enough abilities to protect against the increase In instant solar UV-B radiation. In the deciduous tree species, such as beech, however, the shortening of the productive period may decrease the annual productivity when the solar UV-B will be increased. Less