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樹冠形態の異なるスギ2品種（アヤスギ，シャカイン）および実生苗の一次枝，一次根の形態を比較した．20cmの長さに切断された一次枝，一次根（枝ユニット，根ユニット）の先端断面積（T），基部断面積（B），分岐断面積（S）を測定し，相互の関係を解析した．枝ユニットにおいてはT+S=Bの単純パイプモデルが成立したが，品種間差は認められなかった．一方，根ユニットではT+S≦Bとなり細根の枯死が生じていること...が推測され，樹形のパイプモデルが適用された，このパイプモデルから導かれた細根の枯死率を比較すると実生で大きく，挿し木品種で小さかった．一次枝と二次枝の成長量の比を示すユニットの|T/S比は，一次枝の成長とともに増大することがわかった．頂芽優性の強さを来すと考えられるT/S比の増加率を比較すると，シャカイン＞実生笛＞アヤスギの順に大きかった．また根ユニットではT/S比と一次根の成長との関連性は認められず，したがって頂芽優性は認められなかった．
Branching characteristics of primary branches and primary roots were studied in three types of sugi (Cryptomeria japonica D. Don) differed in their growth patterns and crown form; two cultivars (cv. Ayasugi and cv. Shakain) and a seedling. Primary branches and roots were cut into pieces of 20cm in length, Each piece was classified as a branch unit or root unit. Top cross-sectional areas (T), bottom cross-sectional areas(B), and divergence cross-sectional areas (S) of the units were measured. The simple pipe model relation (T+S=B) was applied to branch units. The pipe model of tree form (T+S≦B)was applied to root units. The results indicated that fine root death occurs more frequently than branch death. Rates of fine root death calculated from 1-(T+S)/B, were high in seedling, and small in cv. Ayasugi and cv. Shakain. Relationships between T/S ratio and B of branch and root units were analyzed in order to compare the strength of apical domillance among the sample trees. T/S ratio of branch units increased proportionally to growth of the primary branch. Differences of the increase rates among sample trees indicated that the decreasing order of strength of apical dominance is as fol1ows:Shakain> seedling>Ayasugi. Apical dolninance was not significant in the root system, as the T/S ratio was not related to the growth of the primary root.show more
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