Foraging for nutrients, responses to changes in light, and competition in tropical deciduous tree seedlings

• Published in: Oecologia 1998-01, Vol.117 (1/2), p.209-216
• Main Authors: Huante, P, Rincon, E, Chapin, F.S. III
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biological competition; Biomass production; Caesalpinia; Caesalpinia eriostachys; Ecosystems Ecology; Foraging; Forest soils; Forestry; Fundamental and applied biological sciences. Psychology; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Heliocarpus pallidus; Malvaceae; plant competition; Plant growth; Plant nutrition; Plant roots; Plants; roots; Soil nutrients; Soil resources; Synecology; Terrestrial ecosystems
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s004420050650

We evaluated (1) the responses of two cooccurring tropical tree species, Heliocarpus pallidus and Caesalpinia eriostachys, to changes in light, (2) the ability of these species to search for and exploit a fertilized soil patch, (3) the relationship between the capacity to forage for a fertilized patch and the capacity to respond to changes in light availability and (4) how the relationship between light and nutrient acquisition influenced the competitive interactions between these species. Plants of the two species were exposed to a factorial combination of high (H) and low (L) light intensity and fertilized (+Fp) and unfertilized (-Fp) nutrient patches for 50 days. Half of the plants from H were then transferred to L (HL treatment), and half of the plants from L were transferred to H (LH). The remaining plants were kept in their original light condition and grown for another 50 days. Plants were grown in these light and patch treatments alone (one plant per pot) and in interspecific competition (one plant per species resulting in two plants per pot). Both species exploited fertilized patches by increasing root biomass and length in the patch. This enhanced plant productivity and growth rate mainly under LH and HH conditions for Heliocarpus and the HH condition for Caesalpinia). When plants in the HH light environment were grown with an unfertilized patch, plant biomass and relative growth rates (RGRs) were even lower than under the LL light environment [(HH-Fp) < LL]. However, the combined activity of shoot and roots when above- and below-ground resources were temporally and spatially heterogeneous influenced plant productivity and growth rate. The benefit from light increase (LH) was reduced when grown with an unfertilized patch. Larger reductions in root biomass, length and density in the patch, and in plant biomass and RGR, were exhibited by Heliocarpus than by Caesalpinia. These results suggest a close relationship between root foraging and light capture, where the benefit of the exploitation of the patch will be reflected in whole-plant benefit, if enough light is captured above-ground. In addition, the results suggest a change in the expected plant responses to light due to heterogeneity in soil nutrients, even though the fertilized patch was only a small proportion of the total soil volume. Leaf characteristics such as specific leaf area responded only to light conditions and not to patchily distributed nutrients. Root characteristics responded mor