Analysis on adaptability of old Cryptomeria japonica tree for water stress using experimental methods

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Position of canopy becomes higher with tree growth. Although tall trees have advantages for light competition, water stress becomes influencing factor for photosynthesis because sap flow resistance in tree body becomes large. In the present study, we tried to prove that increasing the tree height of Cryptomeria japonica result in depression of photosynthesis by experimental method. We also studied on adaptive response in water-relations of needles for increasing water stress in midday. By comparison between the newly developed needles from the scions grafted from tall trees to small seedlings and the needles of the tall tree, we could prove that the photosynthetic activity of the tall trees was depressed by water stress, which resulted in stomatal closure and depression of Rubisco activity. For the adaptive response of needles for water deficit in midday, we found that in situ needles tended to maintain higher water potential than those expected from the Pressure-Volume curve. This adaptive response was resulted from osmotic adjustment and decrease in elasticity of cell wall. This adaptive response was more obvious on the needles of tall trees than ones of small seedlings. This adaptability on water relations may be regarded as one of the reasons why aged Crypyomeria japonica can keep high productivity and grow up to very tall trees more than 50 m.