Water relations and whole-crown transpiration rate of aged Cryptomeria japonica

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In order to clarify the changes in water relations along aging and increasing of tree height, whole-crown transpiration rates, xylem pressure potential and sap flow velocity were measured on a 100-year-old and a 10-year-old Cryptomeria japonica. The results obtained were as follows.(1) The whole-crown transpiration rates were measured with the chamber method. As liner relation was obtained between daily whole-crown transpiration and daily accumulated sap flow velocity, the chamber method was regarded as an available method for the whole-crown transpiration rate.(2) The leaf-mass-based vapor diffusion conductance of crown of the 100-year-old tree were much smaller than those of 10-year-old tree under high air humidity condition. Although the vapor diffusion conductance of the 10-year-old tree sharply decreased along decreasing of air humidity, those of the 100-year-old tree slowly decreased.(3) From the relationship between xylem pressure potentials and sap flow velocities, hydraulic conductivity of each sample tree were determined. The hydraulic conductivity of the 10-year-old tree was smaller than one of the 100-year-old tree under wet soil conditions. The hydraulic conductivity of 10-year-old tree much more increased than the 100-year-old tree along soil dehydration. These results implied that the hydraulic resistance from roots to leaves were larger in the 100-year-old tree than in the 10-year-old tree.(4) In conclusion, it was implied that the lower hydraulic conductivity in the 100-year-old tree than in the 10-year-old tree resulted in the lower crown conductance in the 100-year-old tree, and that the lower crown vapor conductance by stomatal closure resulted in decrease of photosynthetic production in the aged trees.