Phosphorus (P) is an essential nutrient in plant metabolism and frequently limits plant growth and productivity in tropical forests. However, the adaptive plant strategies to efficiently use P on infertile soils remain unclear.
We examined photosynthesis, leaf traits and P fractions in five plant species (Clerodendrum cyrtophyllum, Syzygium bullockii, Psychotria rubra, Schefflera octophylla and Uvaria microcarpa) after six years of nitrogen (N) and P fertilization in a tropical forest in southern China.
Results/Conclusions
Our results show that fertilization did not significantly affect the area-based photosynthetic carbon assimilation. Nitrogen addition had no effect on photosynthetic N-use efficiency (PNUE), photosynthetic P-use efficiency (PPUE), or foliar P fractions, while P addition significantly decreased the PPUE and enhanced the concentrations and relative proportion of metabolic P over other P fractions across the five species.
In these tropical plant species, the higher PPUE in leaves of plants grown in unfertilized soils may be determined by the relatively self-balanced and consistent allocation of P to P-containing metabolic processes. These results suggest that these plant species have evolved adaptive strategies to efficiently use P in P-limited tropical forests; thus additional P availability did not improve leaf photosynthetic rates. We suggest a species-specific mechanism that optimizes the allocation of P among foliar P fractions maintains higher productivity and reduces demand for P at the leaf-level, and this adaptation allows for higher PPUE in P-poor tropical soils.