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スギ心材のアルカリ性化による黒心材形成の遠因を明らかにする目的で，ヤブクグリ，ウラセバルおよびナカムラの3品種を対象に，胸高直径，心材の明度，生材含水率，灰分量，温水抽出物量およびカリウム量を測定し，これらの相互関係を考察した．ヤブクグリの一部およびナカムラのすべての供試木の心材は，黒心を示し弱アルカリ性（pH：7．3～8．0）であった．黒心が弱アルカリ性を示す理由として，黒心には灰分（特にカリウ...ム）が多いためと推測される．つまり，心材の明度は，カリウム量がある限度以下では高くほぼ一定値を示すが，カリウムの増加につれて低下し，ある値のカリウム量ではほぼ一定の低い値を示した．なお，灰分量とカリウム量との間には一次の正の相関関係が認められた．灰分量は，品種によって異なり，さらに同一林分の品種内では胸高直径との間に相関関係が認められた．すなわち，心材中に取り込まれる灰分量は遺伝的な要因と肥大成長に関係する立地条件ないしは環境要因によって決まった．しかし，心材のアルカリ性化への環境要因の関与の度合いは，品種によって差異があると推測された．
Three cultivars of sugi (Cryplmeria japonica), including 20 trees of cv,Yabukuguri, 20 trees of cv.Urasebaru and 22 trees of cv.Nakamura, were examined. Diameter at breast height and lightness, green moisture content, ash content, hot water extractives and potassium content in the heartwood were determined. Correlations between these factors were then discussed. 1) Some cv.Yabukuguri heartwoods and all cv.Nakamura heartwoods was black-colored and weakly alkaline (pH : 7.3～8.0). It is thought that black-heartwood contains so much ash (especially potassium) that it is weakly alkaline. 2) Lightness values of heartwood were constantly high with low potassium content. However the values decreased as potassium content increased. They were then constantly low with high potassium content. 3) There was a significant correlation between ash content and potassium content in heartwood. 4) Ash content in the heartwood varied among cultivars. Furthermore, it was significantly correlated to diameter at breast height within a cultivar grown in the same stand. Namely, the amount of inorganic matters absorbed in heartwood was affected by hereditary factors and locational conditions or environmental factors related to diameter growth. However it is thought that the degree of impact of environmental factors on alkaliztion of heartwood varied among cultivars.続きを見る
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