Decadal insights into phosphorus limitation and adaptive mechanisms in tropical rainforests: a comprehensive nutrient addition study

Tropical rainforests on low-phosphorus (P) soils are highly biodiverse and productive, playing a crucial role in climate change mitigation. However, the degree of P limitation and potential adaptation mechanisms of tropical rainforests remain unclear.Here, we conducted a decade-long field experiment with nitrogen (N) and P additions in a primary and a secondary tropical rainforest. We investigated growth responses of 2,012 individual trees and explored how litter, soil, and microbes contribute to maintaining P availability for plants.We found that P addition enhanced tree growth in both rainforests. P addition also increased the average leaf P concentrations of eight species but reduced P resorption efficiency (PRE) across both rainforests. Soil phosphatase activity and fungal diversity declined with P addition in primary rainforest, the secondary rainforest exhibited higher soil phosphatase activity than the primary rainforest yet maintained lower fungal diversity. Phosphorus addition triggered divergent responses in fungal community composition across both rainforests: characterized by an enrichment of ectomycorrhizal fungi (EMF) and a depletion of arbuscular mycorrhizal fungi (AMF). Notably, EMF functional guilds exhibited habitat-specific differentiation in secondary rainforest— short-distance exploration types increased, while long-distance exploration types declined.These findings reveal that tropical rainforests employ diverse P acquisition strategies, including tree-based mechanisms (e.g., foliar PRE) and soil microbe-mediated processes such as elevated soil phosphatase activity and fungal diversity, and shifts in fungal community composition. This study underscores the importance of P availability in shaping the productivity and resilience of tropical rainforests, providing critical insights into their adaptive responses to nutrient limitations.