Ecophysiological Studies of Broad-leaved Deciduous Trees in Cool-warm Temperate Transition Zone

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Ecophysiology of co-occurring saplings of broad-leaved deciduous trees (Fagus crenata, F. japonica, Srbus alnifolia, S. japonica, Styrax obassia, Fraxinus lanuginosa) and shrubs (Vaccinium oldhammi, Rhododendron semibarbatum, R. obtusum var. kaempferi, Vivurunum wrightii, V. phlebotrichum, Hydrangea hirta), and the phenology, photosynthesis and canopy architecture of Fagus crenata and F. japonica were studied at the Ogawa Scientific Reserve for Natural Forest (36^ﾟ55'N, 140^ﾟ35'E), northernmost part of Ibaraki Prefecture in 1980 and 1981.The annual mean air temperature of two years was 10.8^ﾟC. Relative light intensity of PAR (RLI) in early April was ca. 70% above the shrub layer and 65% at the forest floor, when the leaves of canopy trees did not unfold, and in mid-June the RLIs of two plots decreased in 7 and 3%.Through the measurements of daily courses of water relations in the field and photosynthesis in the laboratory, the following results were obtained. (1) There was a positive … More relationship between transpiration rate and hydraulic conductance. (2) There was two responses against water stress : one was drought avoidance by enlarging bulk modulus of elasticity of cell wall (epsilon) and the other was drought tolerance ; those species had low epsilon. (3) Stomata were sensitive to air-leaf water vapor pressure deficit. (4) Closing of stomata under high light conditions hardly influenced the photosynthetic capacity because of low light-saturated photosynthetic rate. The following distinct differences of ecological characteristics of Fagus crenata and F. japonica were made clear. (1) The phenology of both species was the same. (2) Light-saturated photosynthetic rate and light compensation point of F. crenata were higher than those of F. japonica. (3) The canopy architecture of F. japonica was more flat than that of F. crenata and F. japonica had a lower leaf area index. These results suggested that comparing two species F. japonica was sciophyte and F. crenata was heliophyte. Less