Variation in leaf phosphorus fractions reflects plant adaptations and distribution in low-phosphorus tropical forests

Tropical forests are generally characterized by high species diversity and low soil phosphorus (P) availability. Although tropical plants have evolved adaptations to low soil P availability, we know relatively little about the strategies of different groups of species to efficiently use P, or how these strategies might shape their distributions. We compared the performance of 16 co-occurring species in tropical forests in South China under two soil P regimes. We divided these species into three groups: exotic species, which are not native to South China; eurytopic native species, which occur in both P-limited and P-richer habitats; stenotopic native species, which only occur in low-P habitats. We assessed their growth rates, foliar functional traits and foliar P fractions under experimentally manipulated soil P availability (Control vs. +P). Exotic species exhibited greater plasticity in allocation of leaf P fractions than native species. Compared with native species, exotic species allocated more P to inorganic-P than to ester-P and nucleic-P in P-enriched soil, while they allocated less P to inorganic-P and ester-P in low-P soil. Eurytopic native species responded inconsistently to P addition, indicating that eurytopic native species may employ various strategies to cope with low P availability, whereas stenotopic native species showed only minor changes in leaf P allocation with P fertilization. We distinguished two strategies for plant adaptation to low soil P availability: (1) a P-plastic strategy exhibited by exotic species, in which Pleaf and leaf P-fraction allocation patterns changed substantially with soil P enrichment; (2) a P-conservative strategy exhibited by stenotopic native species, in which Pleaf and leaf P-fraction allocation patterns changed only slightly with soil P enrichment. In conclusion, the distinct strategies exhibited by plants in low-P habitats may determine their distribution and coexistence in tropical regions.