造園樹木の根系の形態に関する研究 : イヌマキ,モクレン,サンゴジュについて

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トレンチ法によって, イヌマキ, モクレン, サンゴジュの根系を調査し, 前報(浅野ら, 1984)のスギ, マテバシイ, ニセアカシアをも含めて比較, 考察した.イヌマキは地上部の割に極めて大きな根系をもち, かつ細根密度も極めて高く, 地上部を力学的に安定的に支えうる根系であり, しかも根の垂直分布が深部まで一様であることから, 深根性樹種と考えた.このイヌマキが同じく深根性のマテバシイと違って移植が容易な理由は, 細根密度の高さに加えて, 太根1本当りの細根数が著しく多いことが挙げられる.これに対して, モクレンは樹高の割に浅い根系であり, かつその根域の上部に根が集中していることから, ニセアカシアと同じく浅根性樹種と考えられる.ニセアカシアと違ってモクレンの移植が困難な理由には, マテバシイと同様に太根1本当りの細根数が少ないことと細根の伸長の悪さが考えられる.サンゴジュは, スギと同じく地上部の割に根系が大きいが, 垂直的にも水平的にも根の分布が根元近くにやや集中することから, 深根でも浅根でもなく, その中間型と考えた.従って, 移植時には根鉢に含まれる根量も多く, さらに2種ともに太根1本当りの細根数が多いことから, 移植が容易になるものと考えられる.

We investigated the root systems of Podocarpus macrophyllus, Magnolia liliflora, and Vibrunum awabuki using a trench method, and discussed the morphological characteristics of their root systems comparing with those of Cryptomeria japonica, Pasania edulis, and Robinia pseudoacacia, reported in our previous paper (ASANO et al., 1984). P. macrophyllus has quite large root system like C. japonica comparing with the others, and the vertical distribution of roots is relatively homogeneous. Therefore, we can conclude that P. macrophyllus is a typical tree of deep root system like P. edulis. Generally speaking, the transplanting of a tree of deep root system is difficult, becase we must cut off the large amount of the root to make the root ball. But, the transplanting of P. macrophyllus is usually successful, because of its quite high density of fine root and its high numeral ratio of fine root/big root. Contrarily, M. liliflora is a typical tree of shallow root system like R. pseudoacacia from the vertical proportion of the root system for the upper parts of tree and the congested distribution of roots to the upper part of the root system. And, the reasons for the difficulty of the transplanting of M. liliflora inspite of the advantage of shallow root system would be the low numeral ratio of fine root/big root and also the poor growth of fine roots from the big roots. V. awabuki is an intermediate type of root system between the shallow and the deep types, and the roots are more congested close to the trunk. C. japonica also belongs to this type despite of its large root system, because of the same reason as V. awabuki. The both species are transplanted with greater success, because of their relatively congested distribution of roots close to their trunks and of their high numeral ratios of fine root/big root.

source:The technical bulletin of Faculty of Horticulture, Chiba University