The low soil phosphorus (P) availability on highly weathered soils in the tropics is often assumed to limit ecosystem productivity. However, recent experiments in diverse tropical forests in Asia, America and Africa have shown that tree growth rate did not strongly responded to P addition. One possible explanation is that tropical tree species adapted to low P soils have means to overcome P scarcity. We tested the following hypotheses using Panamanian tropical tree species: (1) Species adapted to low P soil have a greater growth rate on low-P soil than species adapted to high P soil; (2) interspecific differences in the traits related to P uptake and/or use strategies explain growth patterns. In a pot experiment, we grew 8 species of four congeneric pairs (Cecropia, Cordia, Inga and Tabebuia) on low P soil. The two species in each genus exhibited contrasting P affinities, and were associated with either low or high P soils in central Panama. We determined growth rate, whole-plant P-use efficiency, photosynthetic P-use efficiency, leaf lifespan, P resorption from senescent leaves, P uptake, rhizosphere P availability, root phosphatase activity and fine-root allocation.
Results/Conclusions
Consistent with our hypothesis, growth rate was greater in low-P specialists than in high-P specialists on low-P soil. In three of the four genera, the greater growth rate of low P specialists was largely related to their higher P uptake, while P-use efficiency was more important for Cordia. A linear regression analysis showed that root phosphatase activity and fine-root allocation were positively correlated with nutrient uptake. These results suggest that tree species with high preference for low P soils have a high capacity to scavenge P from soils or to use P more efficiently for growth.