Abstract: Tropical forests, renowned for their exceptional biodiversity, often thrive despite inherently low soil phosphorus (P) availability. However, a comprehensive synthesis of the mechanisms that facilitate the coexistence of diverse species, and how these mechanisms respond to P addition, remains poorly understood. This review consolidates research findings on how tropical forest biodiversity is sustained under low P conditions, how P addition influences the overall biodiversity system, identifies research gaps, and suggests future directions. The relationship between P and biodiversity is complex: while P-limited forests support high diversity, P addition may lead to species disappearance, raising the question of why some forests that maintain high species diversity under P limitation continue to do so, while others experience a decline in diversity following P addition. Despite P limitation, forests can support high species diversity through adaptive strategies such as resource partitioning and P-use efficiency, which enable diverse communities to flourish. In low-P environments, species conserve P through resorption from older tissues and allocation to leaves, promoting photosynthesis and growth. These species exhibit lower specific leaf area and higher leaf dry matter content. While functional diversity is constrained, species diversity remains high as species adopt similar strategies. Specialized root traits, including finer roots and mycorrhizal symbioses, facilitate P uptake in low-P soils. However, P addition may lead to competitive exclusion, with species adapted to P-rich conditions outcompeting low-P specialists. Some species may dominate early successional stages by rapidly utilizing available P, suppressing other species, and reducing biodiversity over time. Anthropogenic P additions, such as agricultural fertilization and erosion, can intensify this effect, further decreasing species diversity and altering community composition, including fauna and microbial components of the forest. Due to the complexity and variability of tropical environments, critical knowledge gaps remain in understanding how diverse forest components, soil organisms, and environmental conditions interact with P addition, particularly at local and regional scales. Long-term studies, especially in less accessible or underfunded tropical regions, are essential to improve understanding of species interactions, resource partitioning, and biodiversity functioning under P-limitation.

Key words: Adaptive strategies, Biodiversity trade-offs, Functional diversity, Nutrient cycling, Nutrient limitation