Fine Root Distribution in a Lower Montane Rain Forest of Panama

In a Panamanian lower montane rain forest we: (1) analyzed the vertical and horizontal distribution of fine roots; and (2) assessed the relationship of fine root mass to thickness of the soil organic layer, soil pH, and soil-extractable nitrogen. The soil in the study area has developed on volcanic ash deposits and was classified as Hapludand. In randomly distributed samples, the median fine root mass (biomass and necromass, diam ≤ 2 mm) to a depth of 100 cm mineral soil was 544 g/m², 41 percent of which was found in the organic layer. Fine root mass was approximately twice as high in the vicinity of stems of the tree species Oreomunnea mexicana (1069 g/m²) and the palm species Colpothrinax aphanopetala (1169 g/m²) and was associated with thick organic layers. The median thickness of the soil organic layer in a larger random sample ( N = 64) was 8 cm with a considerable variation (interquartile range: 7 cm). In these samples, the density of fine root biomass was correlated with the concentration of extractable nitrogen ( r = 0.33, P = 0.011), and on an areal basis, fine root biomass in the organic layer increased with increasing thickness of the organic layer ( r = 0.63, P < 0.001) and decreasing pH_KCl ( r =−0.33, P < 0.01). Fine root biomass in the upper mineral soil did not show significant correlations with any of the studied parameters.