COMPARATIVE-STUDY OF LEAF CARBON GAIN IN SAPLINGS OF THUJOPSIS-DOLABRATA VAR HONDAI AND QUERCUS-MONGOLICA VAR GROSSESERRATA IN A COOL-TEMPERATE DECIDUOUS FOREST

Seasonal courses of leaf CO2 gas exchange in a growing season were exa mined in saplings of Thujopsis dolabrata var. bondai and Quercus mongo lica var. grosseserrata in a cool temperature deciduous forest. Betwee n the two tree species there were no large differences in the light co mpensation point of leaf photosynthesis, except for the season of new leaf expansion. However, light-saturated rates of net photosynthesis w ere obviously high in T. dolabrata var. bondai. Evergreen T. dolabrata var. bondai saplings had large photosynthetic production in two seaso ns, before the emergence of new foliage and after foliage fall of the overstory deciduous trees, because of the significantly high solar rad iant energy penetrating under the forest canopy during the seasons. Sa plings of deciduous Q. mongolica var. grosseserrata were heavily shade d throughout the growing season by foliage of the overstory trees, whi ch resulted in a low daily surplus production. The annual surplus prod uction of leaves in the growing season was estimated to be 2300 mmol C O2 m-2 in T. dolabrata var. bondai and - 100 mmol CO2 m-2, slightly ne gative, in Q. mongolica var. grosseserrata. These results supported th e high survivability of T. dolabrata var. hondai saplings and the high mortality of Q. mongolica var. grosseserrata in the deciduous forest.