Successional status and root foraging for phosphorus in seven tropical tree species

In this study, the impact of localized nutrient patches on above- and belowground growth of tropical trees was examined. Seedlings of seven tree species (Albizia guachapele Kunth (Dugand), Cedrela odorata L., Ceiba pentandra (L.) Gaertn., Cordia alliodora (Ruiz & Pavon) Oken, Dalbergia retusa Hemsl., Gliricidia sepium (Jacq.) Kunth ex Walp., and Swietenia macrophylla King) of varying successional status were used in a greenhouse container experiment. Treatments of homogeneous and heterogeneous P fertilization were used to determine each species' ability to forage morphologically for P. In each pot, root length density, average root diameter, and root length to shoot ratio were measured. It was hypothesized that early successional species would be most effective at taking advantage of the heterogeneous soil environment. This prediction was based on studies showing a high degree of soil heterogeneity in early successional forest environments and the need for plants to take advantage of this variability. The study found great variability in the foraging capacity between species, but the hypothesis that successional status and root foraging ability are related was not supported in the species tested. Overall, five of the seven species examined showed some indication that they were taking advantage of local nutrient patches. In four of these species, increased root length density was detected in P patches (A. guachapele, C. odorata, G. sepium, and S. macrophylla) and one species had decreased root width in the P patches (G. sepium). When comparisons were made between homogeneously and heterogeneously fertilized pots, G. sepium and C. alliodora appeared to take advantage of the heterogeneous resource. Both of these species increased aboveground growth in the heterogeneous pots and C. alliodora also had a decreased root to shoot ratio.