265 Root Architecture in Quercus falcata after Physical Removal of the Radicle Tip or Copper Treatment

Abstract

Quercus falcata acorns were cold-stratified for 120 days and then sown in vermiculite under greenhouse conditions. When radicles were 7 cm long, the root tip was either removed (physically pruned) or dipped in a copper hydroxide solution (copper-treated). Intact root systems were used as control. Seedlings were then moved to a root box to observe root system architectures. The box was built of clear plexiglass 2.5 mm thick, and each face was 25.7 × 35.7 cm. Styrofoam spacers were used to separate faces, and nuts and bolts were placed along edges to hold the root box together. To permit observation of the entire root system, plants were grown in a plane between the plexiglass surface and a nylon sheet that separated roots from the medium (MetroMix 510). At 7, 9, and 11 days after treatment, the entire root system was traced on an acetate sheet, and number of internal and external links and number of secondary and tertiary roots were recorded. Total length, internal and external root links length, were obtained using digital analysis (MacRhizo). Dry weight of roots and shoots was collected at the end of this experiment (day 11). Treatment effects were evident 11 days after treatment. Copper-treated plants had statistically more secondary roots and larger internal link length than control or physically pruned plants. Also, copper-treated plants had smaller mean external link length, showing a more branched root system. Root biomass was similar for all treatments; however, copper-treated plants had smaller root: shoot ratio. This suggests that copper was acting as more than a pruning agent because copper-treated plants showed a different root system architecture compared to physically pruned plants.