Phosphorus Regulation of Decomposition, Microbial Dynamics, and Foliar Chemistry in Moist Tropical Forests

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Despite a widespread belief that low phosphorus (P) availability is a strong constraint on ecosystem dynamics in many tropical forests, direct tests of this belief are rare, and understanding of tropical forest biogeochemistry remains relatively poor. To test this assumption, a phosphorus fertilization experiment will be conducted in lowland moist tropical rainforests located on extremely old soils in southwest Costa Rica. Preliminary work has shown that P availability is poor in these systems, and that low P availability appears to limit the activity of soil microorganisms. This research will follow up on these preliminary data through the use of long-term P fertilization plots which span gradients in soil age and which include at least 3 different dominant canopy trees in these forests. Each individual plot will contain a mature canopy tree at its center, and the trees will contain permanent climbing ropes to provide access to live canopy leaves. In addition to the effects of fertilization on canopy chemistry, the research will monitor processes within the soil and on the forest floor, including soil respiration, litter decomposition, analyses of microbial function and composition, and a suite of soil biogeochemical analyses. This work will advance understanding of how P availability regulates ecosystem processes in lowland tropical forests, with an emphasis on the poorly understood microbial communities. In addition, the investigators seek to maintain these fertilization plots for the long term, and to facilitate collaboration from other scientists interested in using them.