Air Lateral Root Pruning Affects Longleaf Pine Seedling Root System Morphology

Longleaf pine (Pinus palustris) seedlings were cultured with air lateral root pruning (side-vented containers, VT) or without (solid-walled containers, SW). Seedling root system morphology and growth were assessed before planting and 8 and 14 months after planting. Although VT seedlings had greater root collar diameter than the SW before planting, seedling height and ground line diameter were not affected by root pruning 14 months after planting. Root pruning did not affect seedling biomass. However, root pruning changed the patterns of biomass allocation. Before planting, VT seedlings allocated a greater percentage of biomass to roots and less to shoots than SW seedlings. Furthermore, VT seedlings allocated more root biomass to taproots at the expense of the first-order lateral roots (FOLR) and fine roots. This trend of favoring taproots by VT seedlings continued through 14 months after planting. For both types of seedlings, more than 50 percent of the FOLR originated in the top 2.5 cm of the taproot whereas greater than 70 percent of FOLR egressed below 7.5 cm of the root plug after planting. Fourteen months after planting, SW seedlings accumulated greater root biomass within the dimensions of the original root plug than VT seedlings. The VT seedlings had less extent of FOLR spiraling within the root plug than the SW seedlings before and after planting. Less FOLR spiraling and less root biomass increase within the root plug after planting in the VT seedlings may improve the physical stability of the VT longleaf pine saplings.