Predicting future impacts of anthropogenic change on tropical forests requires a clear understanding of nutrient constraints on productivity. We compared experimental fertilization and litter manipulation treatments in an old-growth lowland tropical forest to distinguish between the effects of inorganic nutrient amendments and changes in nutrient cycling via litterfall. We measured the changes in soil and litter nutrient pools, litterfall, and fine root biomass in plots fertilized with nitrogen (N), phosphorus (P), or potassium (K), and in litter addition and litter removal treatments during 7 years. Soil inorganic N and litter N increased in double-litter plots but not in N-fertilized plots. Conversely, litter P and soil pools of P and K increased in fertilized plots but not in the double-litter plots. Soil and litter pools of N and K decreased in the no-litter plots. Changes in litterfall with added nutrients or litter were only marginally significant, but fine root biomass decreased with both the litter and the K addition. Differences between the two experiments are mostly attributable to the coupled cycling of carbon and nutrients in litter. Increased nutrient inputs in litter may improve plant uptake of some nutrients compared to fertilization with similar amounts. The litter layer also appears to play a key role in nutrient retention. We discuss our findings in the context of possible impacts of anthropogenic change on tropical forests.
Bibliographical noteFunding Information:
We wish to thank O. Hernandez, R. Gonzalez, F. Valdez, J. Valdez, G. Perez, F. Zeugin, D. Ureña, A. Vincent, and all Cambridge student volunteers for help in the field. We thank L. Schreeg for information on phosphate sorption, A. Beckermann and J. Staley for statistical advice and M. Heard for useful comments. We are grateful to P. Vitousek and two anonymous reviewers for their helpful suggestions on improving earlier drafts of the manuscript. EJS was funded by a Gates Cambridge Scholarship, a European Union Marie-Curie Outgoing Fellowship MOIF-CT-2005-21728, and a Cambridge Philosophical Society Travel Grant. EVT was funded by the Andrew W. Mellon Foundation, Gonville and Caius College Cambridge and the Department of Plant Sciences, Cambridge. SJW was funded by the Andrew W. Mellon Foundation. SJW, JBY and KEH were funded by a Smithsonian Scholarly Studies Grant. MK was funded by NSF Grant No. 0212386 and JSP was funded by a grant from the Smithsonian Tropical Research Institute.
- fine root biomass
- litter addition
- litter removal
- nutrient limitation
- soil nutrients