Phosphorus Addition Enhances Ecosystem Multifunctionality While Reshaping Multi-Trophic Biodiversity–Function Relationships in a Tropical Cloud Forest

Abstract

Background: Phosphorus (P) availability regulates tropical forest functioning, yet how P enrichment reshapes biodiversity–ecosystem multifunctionality (EMF) relationships remains poorly understood, especially in tropical cloud forests (TCFs), where rising nutrient inputs may shift the balance between ecosystem productivity and biodiversity conservation. We investigated how contrasting P availability alters multi-trophic biodiversity and its relationships with EMF. Methods: Using a three-year field P addition experiment in a TCF at Bawangling, Hainan Island, China, we examined the effects of Control, Low P, and High P treatments on multi-trophic biodiversity. We quantified above- and below-ground biodiversity components and assessed EMF using seven ecosystem functions governing productivity and elemental turnover. Results: P addition increased soil nutrient availability and enhanced EMF, but simultaneously reorganized biodiversity structure by promoting plant functional and bacterial diversity while reducing phylogenetic and fungal diversity. Importantly, P availability shifted the biodiversity dimensions associated with ecosystem functioning: phylogenetic diversity was the dominant biodiversity dimension associated with EMF under ambient P limitation, whereas plant and root functional diversity showed stronger associations with EMF under moderate P addition. Under high P availability, biodiversity–EMF relationships weakened, suggesting a potential decoupling between biodiversity and ecosystem functioning under excessive nutrient supply. P addition was associated with changes in EMF, soil nutrient status, and multi-trophic biodiversity. Our findings suggest that P enrichment may simultaneously enhance EMF and alter the biodiversity–EMF relationships associated with ecosystem functioning. Incorporating P dynamics into ecological monitoring frameworks may therefore improve understanding of tropical forest responses to future nutrient enrichment.