Changes in plant phosphorus acquisition traits across forest biomes along a 3000-m elevational gradient

Tropical forests are frequently constrained by phosphorus (P) limitation, yet how plants maintain their P status under low soil P availability through adjustments in P-acquisition traits remains poorly understood. Across four forest biomes distributed along the elevational gradient, contrasting soil nutrient availability and climatic conditions may alter the relative importance of different P-acquisition traits. In this study, we investigated how plants adjust multiple P-acquisition traits along an elevational gradient to acquire P under contrasting soil P availability. Specifically, we tested whether environmental variation promotes convergence toward a single P-acquisition trait or reshapes the relative importance of multiple coexisting traits. Here, we quantified multiple P-acquisition traits and leaf P status across 61 species-site combinations along a 735–3777 m gradient spanning tropical to subalpine forests. Bulk soil Olsen P concentration ([P]) declined toward lower elevations, while rhizosheath P availability remained relatively stable and leaf [P] was extremely high in tropical forest. The decoupling of leaf [P] and bulk soil Olsen [P] suggested active P mobilization in the rhizosphere and provided indirect evidence for the possibility of a high rhizosheath carboxylate pool. We found that P-acquisition traits varied systematically with biomes along the elevational gradient. The rhizosheath carboxylate pool was highest at the tropical forest in the lowest elevation, that mobilized sufficient P which likely maintained high leaf P status; mycorrhizal colonization rate was consistently great at the subtropical forest in the intermediate elevation, and root branching intensity was consistently high at the subalpine forest in the highest elevation, which was associated with enhanced architectural exploration. These patterns were associated with different environmental drivers: rhizosheath carboxylate pool and root branch intensity were associated more with climatic factors, whereas mycorrhizal colonization was associated with both climatic and edaphic factors. Synthesis. Together, our results show that plants may decouple plant P status from soil available P scarcity through high rhizosheath carboxylate pool. Each forest biome has different P-acquisition traits. By linking species-specific trait expression to environmental drivers, our study provides a mechanistic framework for understanding how forests maintain below-ground nutrient function and species coexistence under shifting environmental conditions.