Species-specific effects of phosphorus addition on tropical tree seedling response to elevated CO2

1. Tropical forest productivity is often thought to be limited by soil phosphorus (P) availability. Phosphorus availability might therefore constrain potential increases in growth as the atmospheric CO2 concentration increases, yet there is little experimental evidence with which to evaluate this hypothesis. We hypothesized that while all species would respond more strongly to elevated CO2 when supplied with extra P, individual species’ responses would also depend on their habitat associations with either high- or low-P soils. We further hypothesized that this effect would be exacerbated by a reduction in transpiration rate under elevated CO2, as transpiration may aid in P acquisition. 2. We used a pot experiment to test the effects of P addition on the physiological and growth response to elevated CO2 of eight tropical tree species with contrasting distributions across a soil P gradient in Panamanian lowland forests. Seedlings were grown in an ambient (400 ppm) or elevated (800 ppm) CO...