Spatial Pattern of Slash Pine Roots and Its Effect on Nutrient Uptake

Nutrient‐uptake models generally assume that roots are uniformly arrayed throughout a soil volume. In high‐fertility soils, departure from this regular distribution is not thought to affect nutrient‐uptake predictions if the roots are randomly arranged, but has the potential to dramatically change nutrient‐uptake predictions if roots are clumped. This study was conducted to document root spatial patterns in a forest ecosystem and to determine if spatial patterns affect how we conceptualize nutrient uptake in low‐fertility soils. Roots were mapped on horizontal faces at 2‐cm depth intervals. Spatial patterns were measured using variance/mean ratio and nearest neighbor distance ( R ) indices. The spatial pattern of slash pine ( Pinus elliottii Engelm.) roots, using either variance/mean or R index, was random and was not affected by either the understory plant community or planting microsite. However, 63% of the pine roots in the check plots were within 0 to 0.6 cm of another pine root, while a similar percentage of pine roots was within 0 to 1.0 cm of another pine root in the weed‐controlled area. At these interroot distances, little interroot competition for K was expected. In contrast, virtually all roots had P‐uptake efficiency of <30%, regardless of understory competition. When nutrient‐uptake efficiency is a function of interroot distance for a random root population in low‐fertility soils, average interroot distance cannot be considered typical of the root population.