© 1996 Heron Publishing—Victoria, Canada
Seasonal branch and fine root growth of juvenile loblolly pine five growing seasons after fertilization
M. A. Sword (1), D. A. Gravatt (2), P. L. Faulkner (3) and J. L. Chambers (4)
1. United States Forest Service, Southern Research Station, Pineville, LA 71360, USA / 2. United States Army Engineers, Waterways Experiment Station, Vicksburg, MS 39180, USA / 3. Louisiana State University, Wetland Biogeochemistry Institute, Baton Rouge, LA 70803, USA / 4. Louisiana State University, School of Forestry, Wildlife and Fisheries, Baton Rouge, LA 70803, USA / Received October 25, 1995
Summary
In 1989, we established two replications of two fertilization treatments in a 10-year-old loblolly pine (Pinus taeda L.) plantation. Between March and September 1993, branch internode and needle fascicle expansion in the upper and lower third
of crowns were measured weekly on three south-facing branches of each of four trees, and new root initiation and elongation
were measured at 10-day intervals in three vertical rhizotrons per plot. In one replication, soil water content was measured
daily.
Fertilization significantly increased the expansion of first flush internodes in the upper crown and first flush needle fascicles
in the upper and lower crown. New root growth was stimulated by fertilization in the second half of the growing season. The
timing of root growth responses to fertilization corresponded to branch phenologies in the upper and lower crown that were
conducive to increased basipetal transport of photosynthate. We conclude, therefore, that new root growth was linked to source–sink
activities in the crown.
Root initiation was greater in the upper than in the lower part of the soil profile; however, as the growing season progressed
and water deficit increased, this relationship was reversed. The effect of soil depth on seasonal root growth was closely
associated with water availability, suggesting that root initiation deep in the soil profile is critical for the continued
production of new roots in environments subjected to short-term, but relatively severe, water deficits.
Keywords:
branch phenology, rhizotrons, source–sink relations, water deficit.
