Responses of young Sitka spruce clones to mechanical perturbation and nutrition: effects on biomass allocation, root development, and resistance to bending

Une machine a « secouer les arbres » a ete mise en place pour etudier les influences d'une perturbation dynamique sur la croissance d'Epinette de Sitka (Picea sitchensis (Bong.) Carr.). Dix clones de huit plantes chacun ont ete secoues pendant 196 jours, a cote de plantes de reference non perturbees. Les arbres ont ete soumis a deux regimes d'alimentation afin de determiner l'influence de la nutrition minerale sur leur comportement mecanique. Aucun effet significatif sur la biomasse de la tige n'a ete observe et la hauteur des plantes soumises au regime d'alimentation le plus eleve semble avoir legerement diminuee. Chez les arbres soumis au regime d'alimentation le plus bas, la section des tiges se trouvant dans le plan de flexion etait plus importante que chez les arbres de reference. Les perturbations mecaniques ont eu pour effet d'accroitre la biomasse des racines principales, ainsi que les rapports biomasse des grosses racines a biomasse des racines fines et biomasse des racines a biomasse des tiges. La section moyenne et la masse des racines principales situees dans le plan de flexion etaient plus elevees chez les arbres perturbes que chez les arbres de reference. Les sections etaient de forme elliptique, de plus grand diametre contenu dans un plan vertical. Ces racines laterales possedaient en outre un systeme de ramification plus riche que les autres. Les effets de clonage ont ete observes dans la plupart des reponses de l'arbre. Les resultats montrent que la resistance a la flexion est accrue chez les plantes secouees soumises au regime d'alimentation le plus bas. Cette adaptation de la croissance a des sollicitations mecaniques permet aux arbres exposes au vent d'ameliorer leur stabilite.

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