OOS 36-1 - Limitation by multiple nutrients revealed by a long-term, large-scale nutrient augmentation experiment in lowland Panama

Thursday, August 11, 2011: 8:00 AM
12A, Austin Convention Center
Kyle E. Harms1, Joseph B. Yavitt2, Milton N. Garcia3, Michael Kaspari4 and S. Joseph Wright3, (1)Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, (2)Natural Resources, Cornell University, Ithaca, NY, (3)Smithsonian Tropical Research Institute, Panama, (4)Department of Biology, University of Oklahoma, Norman, OK

Nutrient limitation of ecological or ecosystem-level processes can be determined directly via manipulation of nutrient elements.  Partly owing to a variety of logistical challenges (e.g., environmental spatial heterogeneity, long-lived trees, diverse species composition), this straight-forward experiment has been attempted in relatively few intact, old-growth tropical forests.  We initiated a nutrient-addition press-experiment in 1998 in lowland moist forest of the Barro Colorado Nature Monument (Gigante Peninsula), Republic of Panama.  The experiment comprises factorial NPK-additions and a separate micronutrient treatment, each replicated four times.  Each fertilized and control plot is a 0.16-ha square within which we have been assessing components of net primary productivity (e.g., fine-root dynamics, litterfall, trunk diameter growth) and other ecosystem processes (e.g., decomposition), several of which have been monitored for over a decade.   


At least one monitored ecological or ecosystem-level process has responded to each of the three augmented macronutrients or to the addition of micronutrients.  For example, the addition of K was associated with decreases in stand-level fine-root biomass that appeared after 2 yr and persisted for at least a decade.  The addition of P was initially (after 4 yr) associated with a significant increase in the reproductive fraction of litter and later (after 10 yr) with a marginally significant increase across all litter fractions.  The addition of K and N together was associated with significant increases in growth rates of stems 1- to 10-cm diameter at breast height.  One or more micronutrients were associated with enhanced leaf-litter decomposition, K enhanced cellulose decomposition, and P enhanced both.  Our long-term, large-scale nutrient augmentation experiment suggests that key ecological and ecosystem-level processes in late-secondary to old-growth tropical forests on highly weathered, but relatively fertile mainland soils may nevertheless be limited by multiple elements.

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