Primary productivity in tropical forests is widely assumed to be limited by phosphorus availability, but support for this paradigm remains limited and equivocal. Biogeochemical theory predicts that phosphorus limitation should be prevalent on old, strongly weathered soils, but experimental manipulations have failed to detect a consistent response to phosphorus addition in diverse lowland tropical forests. To investigate this, we measured the growth rates of almost 19,000 individual trees in 541 tree species in a network of plots spanning a strong phosphorus gradient in Panama. We then used hierarchical models to quantify the responses of individual species and entire communities to phosphorus availability.
Results/Conclusions
We find widespread phosphorus limitation at the level of individual species, which strengthens markedly below a threshold of two parts per million exchangeable soil phosphate. However, this species-specific phosphorus limitation does not translate into a community-wide growth response, because a subset of species are adapted to infertile soils and grow rapidly despite extremely low phosphorus availability. Stand-level growth rates are therefore similar across the entire phosphorus gradient, despite pervasive phosphorus limitation of individual species. These results redefine our understanding of nutrient limitation in diverse plant communities and have important implications for attempts to predict the response of tropical forests to environmental change.