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Controls over foliar N:P ratios in tropical rain forests
Alan R Townsend1, Cory C Cleveland, Gregory P Asner
1INSTAAR and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309, USA. alan.townsend@colorado.edu
Ecology
|May 11, 2007
Summary
Tropical forest foliar nitrogen:phosphorus (N:P) ratios are highly variable, primarily due to species differences, not latitude or rainfall. Understanding this species variability is key for accurate ecosystem process predictions.
Area of Science:
- Ecology
- Biogeochemistry
- Plant Physiology
Background:
- Foliar nutrient concentrations correlate with soil nutrients, informing ecosystem process predictions.
- Ecological stoichiometry studies highlight elevated foliar nitrogen:phosphorus (N:P) ratios in tropical forests, suggesting they are N-rich and P-poor.
- This generalization overlooks tropical heterogeneity in soil fertility, climate, and high plant species diversity.
Purpose of the Study:
- To investigate the primary drivers of variation in foliar N:P ratios within tropical forests.
- To analyze original foliar N and P data from 150 tree species in Costa Rica and Brazil.
- To synthesize existing literature for a comprehensive understanding of tropical foliar stoichiometry.
Main Methods:
- Collected foliar N and P data from 150 mature canopy tree species across Costa Rica and Brazil.
- Synthesized existing literature on tropical foliar N:P ratios.
- Analyzed relationships between foliar N:P, latitude, precipitation, soil properties, season, and species.
Main Results:
- No significant relationship found between foliar N:P ratios and latitude or mean annual precipitation within the tropics.
- Seasonal variation in foliar N:P was observed, with a 25% difference between wet and dry seasons in Costa Rica.
- Foliar N:P ratios varied with soil P availability and soil order, but species-level variation was the most prominent feature.
Conclusions:
- Species variability is the dominant factor influencing foliar N:P ratios in tropical forests.
- Unlike marine systems, tropical forest N:P stoichiometry is not tightly constrained.
- Accurate inference of tropical ecosystem processes requires accounting for species diversity and their varied nutrient requirements.
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