Host: The Japanese Forestry Society
The aim of this study is to estimate the ability of acclimation to high irradiance of four fruit tree species planted at open site by using chlorophyll fluorescence methods. We discussed the differences in the acclimation capacity to high irradiance among species in terms of photoprotective mechanisms associated with electron transport rate (ETR) and thermal energy dissipation (NPQ) between shade-grown seedlings and open-planted seedlings. In addition, to evaluate the susceptibility to photoinhibition of the shade-leaves of each species, the extent of photoinhibition of PSII after exposure to full sunlight and subsequent recovery was followed by means of chlorophyll fluorescence recording. The ability of acclimation to strong irradiance differed among four fruit tree species. Bouea oppositifolia showed high susceptibility to photoinhibition by strong irradiance and low survival rate of open planted seedlings. Bouea oppositifolia was considered to have low ability to acclimation to full sunlight. Ficus enhanced light-saturated electron transport rate and decreased thermal energy dissipation in open leaves compared with shade leaves. It was suggested that Ficus had the highest capacity of acclimation to strong irradiance among four fruit tree species. Though Parkia speciosa increased thermal energy dissipation in open leaves compared with shade leaves, light-saturated ETR was the lowest both in shade leaves and in open leaves among measured species. These results mean that Parkia speciosa is not suitable for planting at open site. Pometia pinnata showed higher thermal energy dissipation in open leaves compared with shade leaves, while electron transport rate decreased markedly and the susceptibility of photoinhibition (indicated by declining of qP) increased in open leaves. However Pometia pinnata demonstrated comparative high survival rate in open planted seedlings. From these results, it was considered that Pometia pinnata might have another mechanisms for acclimation to strong irradiance, such as production of new leaves under high irradiance.
