The composition and diversity of rhizosphere microbial communities may be due to root–soil–microbial interactions. The fine root functional traits and rhizosphere soil environmental factors of 13 representative plants in the Bawangling tropical cloud forest of Hainan Island were measured, to assess the key factors driving plant rhizosphere microbial communities. Illumina MiSeq sequencing technology was used to sequence the v3-V4 region of the 16SrDNA gene of 13 plant rhizosphere soil bacteria and the ITS1 region of the fungal ITSrDNA gene. Results showed that there were 355 families, 638 genera, and 719 species of rhizosphere soil bacteria as well as 29 families, 31 genera, and 31 species of rhizosphere soil fungi in the tropical cloud forests. The fine root traits, such as root phosphorus content, the specific root length and specific root area, were significantly negatively correlated with the Faith-pd indices of the bacterial community but were not correlated with the diversity of fungi communities. The soil pH was significantly and positively correlated with the Chao1 index, OTUs, Faith-pd and Simpson indices of the bacteria and fungi communities. The soil available phosphorus content was significantly and negatively correlated with the bacteria Simpson and the fungus Faith-pd indices. ABT analysis showed that soil pH and soil available phosphorus were the most important environmental conditions contributing to the rhizosphere bacterial and fungi communities, respectively. Our findings demonstrate that the soil environments had more influence on rhizosphere soil microbial diversity than the fine root functional traits.

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.