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.