Decadal nutrient addition reveals phosphorus limitation and its adaptive mechanisms in tropical rainforests

Tropical rainforests on low-phosphorus soils are highly biodiverse and productive, playing a crucial role in climate change mitigation. However, the degree of phosphorus limitation and potential adaptation mechanisms of tropical rainforests remain unclear.

Here, we conducted a decade-long field experiment with nitrogen (N) and phosphorus (P) additions in primary and secondary tropical rainforests. We investigated growth responses of 2012 individual trees and explored how litter, soil, and microbes contribute to maintaining P availability for plants.

We found that the P addition alone enhanced tree growth in both rainforests. Adding P (alone or with N) increased the average leaf P concentrations of eight species but reduced P resorption efficiency (PRE), soil phosphatase activity, and fungal diversity in the two forests. Phosphorus addition triggered divergent responses in fungal community composition across both forests: characterized by an enrichment of ectomycorrhizal fungi (EMF) and a depletion of arbuscular mycorrhizal fungi (AMF). Crucially, EMF functional guilds differentiated: short-distance exploration types increased significantly, while long-distance types declined.

These findings reveal that tropical rainforests adapt to P limitation through microbially mediated strategies: enhanced soil phosphatase activity for organic P mineralization and shifts toward EMF functional groups specialized in P acquisition. Reduced PRE indicates lower reliance on internal P recycling under elevated P availability. This study underscores the importance of P availability in shaping the productivity of tropical rainforests, providing critical insights into their adaptive responses to nutrient limitations.