Pervasive phosphorus limitation of tree species but not communities in tropical forests

In lowland tropical forests in Panama, widespread species-level phosphorus limitation of tree growth is not reflected in community-wide growth or biomass owing to the presence of a few species tolerant of low phosphorus availability. Foods of the forest Primary productivity in tropical forests is widely assumed to be limited by phosphorus availability, but evidence is equivocal. Benjamin Turner and colleagues examine the growth rates of tropical tree species along a steep gradient of soil phosphorus availability in Panama, and find that most species grow faster when soil phosphorus availability is higher. No such response is seen at the community level, however, because a subset of species that have adapted to infertile soils grow rapidly despite extremely low phosphorus availability. Phosphorus availability is widely assumed to limit primary productivity in tropical forests 1 , 2 , but support for this paradigm is equivocal 3 . Although biogeochemical theory predicts that phosphorus limitation should be prevalent on old, strongly weathered soils 4 , 5 , experimental manipulations have failed to detect a consistent response to phosphorus addition in species-rich lowland tropical forests 6 , 7 , 8 , 9 . Here we show, by quantifying the growth of 541 tropical tree species across a steep natural phosphorus gradient in Panama, that phosphorus limitation is widespread at the level of individual species and strengthens markedly below a threshold of two parts per million exchangeable soil phosphate. However, this pervasive species-specific phosphorus limitation does not translate into a community-wide response, because some species grow rapidly on infertile soils despite extremely low phosphorus availability. 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.