Carbon translocation patterns associated with new root proliferation during episodic growth of transplanted Quercus rubra seedlings
Joshua L. Sloan (1) and Douglass F. Jacobs (1, 2)
1. Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Purdue University, 715 West
State Street, West Lafayette, IN 47907-2061, USA / 2. Corresponding author () / Received June 28, 2007; accepted November 19, 2007; published online May 1, 2008
Summary
Patterns of carbon allocation in northern red oak (Quercus rubra L.), characterized by episodic growth through recurrent single-season flushing, vary by growth stage. To examine post-transplant
timing and carbohydrate sources for new root growth, dormant, bare-root, half-sibling northern red oak seedlings were transplanted
to pots and placed in a favorable growth chamber environment. Unlabeled seedlings were harvested at transplant and at the
bud swell stage. After leaf emergence, seedlings were exposed to 14CO2 at the linear shoot, linear leaf or lag growth stages. Seedlings were then placed in a growth room for 48 h to allow for
translocation of 14C-labeled current photosynthate and its stabilization in sink component plant parts. Seedlings were subsequently harvested
and tissue 14C:12C ratio analyzed. New root growth began during the linear shoot growth stage. However, no increase in 14C:12C ratio was found in new roots until the linear leaf and lag growth stages, indicating a downward shift in translocation of
current photosynthate to fuel new root growth. In old roots, 14C:12C ratio increased at the lag stage. Our results indicate that both stored carbohydrates and current photosynthate contribute
to new root growth of transplanted northern red oak seedlings; stored carbohydrates promote initial new root proliferation,
whereas current photosynthate assumes a greater role as new leaves mature and the flush terminates. Optimizing nursery practices
to increase carbohydrate reserves may reduce the time required to establish root–soil contact and facilitate early post-planting
survival.
